I dumped 11 popular Google apps on my Android phone for these open-source alternatives.
(www.androidauthority.com)
A lot of the Keep replacements I see posted are just fancy text editors full of markdown formatting junk
Keep is specifically for taking notes, not just for grocery lists. But personally, I use Obsidian.md with a specific note full of checkboxes, and use SyncThing to sync the folder/vault between devices. That being said, since you don't want markdown you probably wouldn't be interested in it