Removed app is still available - how to remove it?

If you are trashing an app manually, then you have to delete it's supporting files. Those could be in Application Support, Contextual Menu Items, Preferences, Receipts etc folders.

Use apps like AppZapper to uninstall apps completely with all the related files. It's a paid app, but it works very well.

To remove all entries in Finders "Open with" for apps that no longer exist, open Terminal and enter

/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user

This takes a little while. Then enter

killall Finder

After that, the invalid entries have been removed from the "open with" menu in Finder. This should work with in macOS versions.

Note that the menu list needs to be rebuilt, so there might occur a slight delay when using it at first.

Unfortunately, the "open with" entries in Finder are often left long after having deleted the app that is listed there. I think that's a bug in macOS.