I was looking for something like this just a few days ago. Ended up going with Flow[1], an open source Android app, because I wanted something that I could enter data on from my phone and run completely locally there. I don't yet have Tailscale running, or some other solution to access my homelab on the go. But it's great to see more and more software designed to run on people's local networks. And from the screenshots ExpenseOwl is the next tool I'd try if Flow doesn't work out... Getting Tailscale or a similar solution up and running is also on the to-do list.
I know other people want direct integration with banking APIs, but for me it's actually a feature to have to enter everything manually. I'm deliberately working on better spending habits, and having a local set of data with me which is actually sometimes ahead of my bank in terms of cleared transactions is good. It means I build the habit of entering and categorizing each time I spend money, and it means I have to regularly reconcile accounts. It's only a hypothesis, but I suspect in the era of checkbooks the practical fact of having to keep up the books manually enforced better spending habits.
[1a]: https://play.google.com/store/apps/details?id=mn.flow.flow
[1b]: Also, github: https://github.com/flow-mn/flow
N.B. There's another expense tracker on the Play store, also called "Flow", which AFAICT isn't open source.