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

I just started using KitchenOwl for this. It can be a little clunky, but it suits my purposes well.
Pros:

• self hostable
• multiple grocery lists
• categories and sorting are customizable (so I can put the categories in the order I shop in)
• sync across devices near instantaneous
• web and desktop interface

Cons:

• can be a little slow to add items. You can't just add text, you have to wait until the search is complete
• does not automatically combine the same item together
• occasionally when I switch to the app and mark an item complete, it doesn't take. Only happens on the first item on open and I just click it away again, so not a huge deal.

I really like koffan.

I softly suggest using a messaging app for this, like a signal thread where you delete items as they're picked up.

I went on a similar search when I ditched big tech a few years ago. I tried most of the options that were available at the time but I'm sure the landscape has changed now.

I've been happy with the shopping list manager built into https://github.com/TandoorRecipes/recipes with https://github.com/kitshn-app/kitshn