There is a huge number of alternatives, depending on what features you need. Joplin is probably the most famous open-source alternative. You can also subscribe to Joplin Cloud to have e2e-encrypted note synchronization between devices.
If you don’t need a web clipper, look into Standard Notes (FOSS and e2e encryoted, also available via web interface - that’s what I use ATM), Simple Notes (FOSS but not encrypted), Obsidian (great but maybe a bit overkill and expensive if you want to sync) or Anytype (also a bit overkill and still in beta, but also very promising)