Just watched a video on the topic

https://odysee.com/@RTP:9/%F0%9F%8F%A6-banking-apps-on-grapheneos:d

As the comments suggest you better get a lineage os supported phone. If it is not available check telegram channels that go with the name "YOUR-PHONE-MODEL updates" and check some roms on there. Look for official roms with open source code and ask in the support channels if they support exploit protection

xapo works with a rooted phone but revolut doesn't. no idea about custom roms, i would assume no root no problem.