I am a very, very happy user of Joplin! I use it all the time to organize mostly code snippets and work instructions for my projects. So if nothing happens with these, no hard feelings! Still I keep stepping on those same little rocks in my shoe and I thought I'd write them down here:
1 Copying a line of inline code shouldn't copy its surrounding formatting code. I you select the line of code without being super precise, you'll get on your clipboard something like:
'npm i ...'
  ;
2 There used to be a markdown editor. Now i can toggle editors but I have no idea what it's for. There is no markdown anymore to be edited.
3 There is no warning when dragging a note to another parent. This can happen very easily without even noticing it. Just a popup with the message: "Do you want to copy A to B?" with Ok and Cancel button would save a lot of head-scratching 'where the hell is my note?!'
4 Clearly marked "Search all" button and show search scope when using it.
5 There is no File, Open option. I actually don't really know where my notebook is stored. Could also just be an Info option under Notebook in the menu that shows the path. I don't couldn't find the path in the menu options anywhere.
6 I always reload a note to see that it recognized and converted links. This should just happen when the link is pasted, or space or return key is hit.
7 Language selector dropdown when adding code blocks. It does work well already but I tend to use the same languages so it would be nice to pre select my common ones with an option for 'other' to specify another language.
2.) See WYSIWYG Toggle for how to toggle between Markdown and Rich Text editors.
3.) Changing notebook appearance when dragged over may be more helpful. Another option is pressing Ctrl+Shift+P then using moveToFolder to type or select a notebook.
3: Yes I think this isn't handled very well, but I don't think a Popup would be necessary the best UX. At least for the Desktop version:
There is no Animation, Highlighting and other visual Feedback, which imho would be the proper way to solver this. I think an optional Popup could be viable, too: "Hey want to move this Note to X? Yes, No, Don't ask me again". Users who use Drag and Drop a lot could disable it. Another Option could be to show a short Notification somewhere "Copied Note X to Y", this way Users can quickly find the note again. The other alternative is to disable Drag and Drop, if not implementing a proper UX? However not sure how this is implemented in Mobile.
4: Agree. Using a Plugin feels like a workaround, I think either displaying the context or highlighting it in the sidebar could be a possibility.
5: Besides the already mentioned way: Help > Open profile directory
7: You have a drop-down? I mostly use the richtext editor, while I like Markdown I also like rendered links, images, tables, etc. and I don't saw any Drop-down there. Which may relate to 2, having two editors with different capabilities is somewhat confusing.