Moneybuster works with nextcloud cospend and ihatemoney, maybe that's worth looking at

Splid is great. Simple yet feature-rich if you need it. If you want to create many different groups for splitting it’s just a small one time fee instead of monthly. If two groups is fine or you just want to join groups it’s free.

And best of all: there is no need for an account! In fact there is no account you could create.

Update: Missed in which community I’m in. The App sadly isn’t FOSS and isn’t in the fdroid-store. But it doesn’t change my opinion about it :)

What’s wrong with Splitwise? The only other alternative I know is Tricount but it’s worse in all aspects

I use moneybuster synchronized to my nextcloud, but it can synch to ihatemoney. Maybe it has more features than you want.