The problem is not obtaining the APK, that's the easy part. The hard part with a lot of online banking apps (as well as apps like Netflix) is that they use (and require) Google SafetyNet to ensure that your ROM is "safe" (i.e. hasn't been tampered with). The guys over at the MicroG project are trying to find ways around that but it's really a cat-and-mouse game. Last time I tried (which, admittedly, was quite a while ago), neither my online banking app nor Netflix worked for me on a custom ROM.
Hmm. I have MicroG since months and last i checked Netflix worked just fine.
That's good news! I assume you're using Magisk for root?
Actually no. I'm using Lineage su addon.
Nah, I found my banking app (Barclays UK), just crashed with MicroG.
Cheers, I'll look into that!
I had the same issue with my bank, but I resolved it using the F-Droid app "Yalp Store", which wraps the playstore. Now I have my banking app on my phone!
It's not FOSS, but even on my Linux PC I have binary blobs for drivers and stuff. It's good enough for me, it might work for your app too