@QuasirandomFreda (turnipsoft.com) may be the best option. With v5, Jim Chapman removed the ads last year, so it's even better.
It also can connect to your calibre server.
An old version (with ads) is also available Amazon store.
I stopped using Freda a long time ago, because it crashed too often and had problems with modern files. But it seems to have improved.
If all else fail, maybe stick to a browser based reader like:
play.google.com/books
It actually is very good.
There is also an open source electron based standard developed by edrlab.org, they do not have an android port, but provide the technology for their partner like Vivlio and others publishers. Any reader based on that is sure to be very compatible, but maybe too slow for an old Kindle Fire.