Paisa was open source. The developer then removed it I guess. The repo you linked doesn't host the app. ~~The developer said it's used for reporting issues~~. Edit : The repo is private

Cashew is open source GPL licensed. But it uses Google libraries which I guess prevents it from being on f-droid. Last time I used Cashew, the premium features notifications could be ignored and the app could be used completely for free, I'm unsure if that was changed though.

I found another app but it's not on f-droid, you'll have to use Obtainium - Monekin

To be honest I can't give any answer, but I tried Paisa and it felt sketchy, so I decided to use GNUCash.

I am using https://play.google.com/store/apps/details?id=vopo.easyhomefinance

It was open source but can't find source now

I had used Hibiscus in the past. The source code can be found here: https://github.com/willuhn/hibiscus