I've been doing some work in my own branch, and while I've been able to build, run and commit, it looks like npm install is not installing all the dependencies:
elsiehupp@Elsies-MacBook joplin % npm install
> joplin@1.0.0 postinstall /Users/elsiehupp/Repositories/joplin
> cd Tools && npm i && cd .. && cd ReactNativeClient && npm i && cd .. && cd ElectronClient && npm i && cd .. && cd CliClient && npm i && cd .. && gulp build
audited 186 packages in 1.477s
4 packages are looking for funding
run `npm fund` for details
found 2 vulnerabilities (1 low, 1 high)
run `npm audit fix` to fix them, or `npm audit` for details
> Joplin@0.8.0 postinstall /Users/elsiehupp/Repositories/joplin/ReactNativeClient
> patch-package --patch-dir ../patches/shared && jetify && npm run build
patch-package 6.2.2
Applying patches...
htmlparser2@4.1.0 ✔
Jetifier found 1332 file(s) to forward-jetify. Using 4 workers...
> Joplin@0.8.0 build /Users/elsiehupp/Repositories/joplin/ReactNativeClient
> gulp build
[00:34:48] Working directory changed to ~/Repositories/joplin
[00:34:48] Using gulpfile ~/Repositories/joplin/gulpfile.js
[00:34:48] Starting 'build'...
[00:34:48] Starting 'copyLib'...
[00:34:49] Finished 'copyLib' after 564 ms
[00:34:49] Starting 'tsc'...
[00:35:03] Finished 'tsc' after 14 s
[00:35:03] Starting 'updateIgnoredTypeScriptBuild'...
[00:35:03] Finished 'updateIgnoredTypeScriptBuild' after 797 ms
[00:35:03] Finished 'build' after 15 s
npm WARN @react-native-community/datetimepicker@3.0.3 requires a peer of react-native-windows@>=0.62 but none is installed. You must install peer dependencies yourself.
npm WARN babel-eslint@10.1.0 requires a peer of eslint@>= 4.12.1 but none is installed. You must install peer dependencies yourself.
npm WARN react-native-fs@2.16.6 requires a peer of react-native@^0.59.5 but none is installed. You must install peer dependencies yourself.
npm WARN react-native-fs@2.16.6 requires a peer of react-native-windows@^0.57.2 but none is installed. You must install peer dependencies yourself.
audited 1204 packages in 24.832s
27 packages are looking for funding
run `npm fund` for details
found 5 vulnerabilities (4 low, 1 high)
run `npm audit fix` to fix them, or `npm audit` for details
> Joplin@1.3.3 postinstall /Users/elsiehupp/Repositories/joplin/ElectronClient
> npm run build && gulp electronRebuild
> Joplin@1.3.3 build /Users/elsiehupp/Repositories/joplin/ElectronClient
> patch-package --patch-dir ../patches/shared && patch-package --patch-dir ../patches/node && gulp build
patch-package 6.2.2
Applying patches...
htmlparser2@4.1.0 ✔
patch-package 6.2.2
Applying patches...
sax@1.2.4 ✔
[00:35:12] Using gulpfile ~/Repositories/joplin/ElectronClient/gulpfile.js
[00:35:12] Starting 'build'...
[00:35:12] Starting 'compileScripts'...
[00:35:12] Starting 'compilePackageInfo'...
[00:35:12] Starting 'copyPluginAssets'...
[00:35:12] Starting 'copyTinyMceLangs'...
[00:35:12] Starting 'updateIgnoredTypeScriptBuild'...
[00:35:12] Starting 'compileExtensions'...
Copying to /Users/elsiehupp/Repositories/joplin/ElectronClient/tools/../gui/note-viewer/pluginAssets
Copying /Users/elsiehupp/Repositories/joplin/ElectronClient/tools/../../Modules/TinyMCE/langs => /Users/elsiehupp/Repositories/joplin/ElectronClient/tools/../node_modules/tinymce/langs
[00:35:13] Finished 'compileScripts' after 991 ms
[00:35:13] Finished 'compilePackageInfo' after 991 ms
[00:35:13] Finished 'updateIgnoredTypeScriptBuild' after 1.01 s
[00:35:13] Finished 'compileExtensions' after 1.02 s
[00:35:13] Starting 'copyLib'...
Copying to /Users/elsiehupp/Repositories/joplin/ElectronClient/tools/../pluginAssets
[00:35:14] Finished 'copyTinyMceLangs' after 1.11 s
[00:35:14] Finished 'copyPluginAssets' after 1.19 s
[00:35:14] Finished 'copyLib' after 694 ms
[00:35:14] Finished 'build' after 1.72 s
[00:35:15] Using gulpfile ~/Repositories/joplin/ElectronClient/gulpfile.js
[00:35:15] Starting 'electronRebuild'...
Running: "/Users/elsiehupp/Repositories/joplin/ElectronClient/tools/../node_modules/.bin/electron-rebuild"
[00:35:16] Finished 'electronRebuild' after 1.47 s
npm WARN ajv-keywords@3.4.1 requires a peer of ajv@^6.9.1 but none is installed. You must install peer dependencies yourself.
npm WARN babel-eslint@10.1.0 requires a peer of eslint@>= 4.12.1 but none is installed. You must install peer dependencies yourself.
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: 7zip-bin-linux@1.3.1 (node_modules/7zip-bin-linux):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for 7zip-bin-linux@1.3.1: wanted {"os":"linux","arch":"any"} (current: {"os":"darwin","arch":"x64"})
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: 7zip-bin-win@2.2.0 (node_modules/7zip-bin-win):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for 7zip-bin-win@2.2.0: wanted {"os":"win32","arch":"any"} (current: {"os":"darwin","arch":"x64"})
audited 1481 packages in 11.708s
16 packages are looking for funding
run `npm fund` for details
found 9 low severity vulnerabilities
run `npm audit fix` to fix them, or `npm audit` for details
> joplin@1.3.0 postinstall /Users/elsiehupp/Repositories/joplin/CliClient
> npm run build && patch-package --patch-dir ../patches/shared && patch-package --patch-dir ../patches/node
> joplin@1.3.0 build /Users/elsiehupp/Repositories/joplin/CliClient
> gulp build
[00:35:23] Using gulpfile ~/Repositories/joplin/CliClient/gulpfile.js
[00:35:23] Starting 'build'...
[00:35:23] Starting 'prepareBuild'...
[00:35:23] Finished 'prepareBuild' after 724 ms
[00:35:23] Starting 'compileExtensions'...
[00:35:23] Finished 'compileExtensions' after 4.18 ms
[00:35:23] Starting 'copyLib'...
[00:35:23] Finished 'copyLib' after 92 ms
[00:35:23] Finished 'build' after 824 ms
patch-package 6.2.2
Applying patches...
htmlparser2@4.1.0 ✔
patch-package 6.2.2
Applying patches...
sax@1.2.4 ✔
audited 906 packages in 6.316s
4 packages are looking for funding
run `npm fund` for details
found 10 vulnerabilities (8 low, 2 high)
run `npm audit fix` to fix them, or `npm audit` for details
[00:35:26] Using gulpfile ~/Repositories/joplin/gulpfile.js
[00:35:26] Starting 'build'...
[00:35:26] Starting 'copyLib'...
[00:35:26] Finished 'copyLib' after 97 ms
[00:35:26] Starting 'tsc'...
[00:35:39] Finished 'tsc' after 13 s
[00:35:39] Starting 'updateIgnoredTypeScriptBuild'...
[00:35:39] Finished 'updateIgnoredTypeScriptBuild' after 652 ms
[00:35:39] Finished 'build' after 14 s
npm WARN @typescript-eslint/eslint-plugin@2.10.0 requires a peer of eslint@^5.0.0 || ^6.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN @typescript-eslint/parser@2.10.0 requires a peer of eslint@^5.0.0 || ^6.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN eslint-plugin-import@2.20.2 requires a peer of eslint@2.x - 6.x but none is installed. You must install peer dependencies yourself.
npm WARN eslint-plugin-react@7.18.0 requires a peer of eslint@^3.0.0 || ^4.0.0 || ^5.0.0 || ^6.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN eslint-plugin-react-hooks@2.4.0 requires a peer of eslint@^3.0.0 || ^4.0.0 || ^5.0.0 || ^6.0.0 but none is installed. You must install peer dependencies yourself.
audited 852 packages in 67.763s
26 packages are looking for funding
run `npm fund` for details
found 4 low severity vulnerabilities
run `npm audit fix` to fix them, or `npm audit` for details
elsiehupp@Elsies-MacBook joplin %