The update could not be installed. Please make sure there are no other copies of Zotero running on y
I'm encountering this issue on my Deepin 20.8 system (linux distribution). I know that there are already many similar issues on the forum. But my Zotero was installed from tarball as suggested in the download page.
On a Debian-based system, you may want to just use the zotero-deb package:
https://www.zotero.org/support/installation#linux