I don't know what features you're looking for but I use nextcloud notes. It's really great for my uses, I keep categorized shopping lists, to do lists, email drafts, etc all in one app. I can access it trough the Android app on my phone and through the web frontend on my nextcloud instance from anywhere.
Orgzly app for android. It is based on org-mode plain text files and support sync via WebDav. Org-mode is one of the oldest format of todo files and have a huge community/plugins/guides/etc.
Because it is plain text in very popular format it may be easily migrated between different cloud storages and may be edited from PC tooo in a any text editor.
I don't think it's open source but we use our groceries. Just links to an email only no password. They just send you a code when you link the email to a new app. It's also cross platform if that matters at all. Also requires no permissions granted to run and only requests a camera permission to scan barcodes.