I've made the mistake of downloading and replacing the version of Joplin that worked with my OS (Big Sur) with the latest (3.5.11) and it doesn't work. Can I get the legacy version back somehow?
Also, this is my first post here, and I'm hoping I've done it in the right way/spot. If not, I'm sorry.
I do not use a Mac but it appears that Electron (the framework used to create Joplin) dropped support for Big Sur (11) with Electron v38.0.0.
So, looking at the Joplin release notes, the last published version before Joplin upgraded to Electron v39 was the pre-release Joplin v3.5.6 (Electron v37.4.0). If I have read all these notes correctly this is the last version of Joplin you will be able to install.
The link above points to the entry for v3.5.6 in the Releases area of the Joplin GitHub (as mentioned above by @Thom).