I was answering this question from you, not asking for advice:
> what financial services companies are inaccessible via a web browser?
Yes the fix is obvious if it was a problem. I thought I made it clear I think it is a net increase in security, and so isn't a problem, for me anyway. Even if it was a problem, your throw away suggestion of "just move to another bank" is not so easy if you've borrowed money from the bank.
None of this has anything to do with topic being discussed - which is should Google allow side loading of unsigned apps. You seem to be positively enthusiastic about handing the keys to your life and assets to Google and / or Apple. The comments you see here are from people who aren't so sanguine about it. You look to be dismissive of their concerns. I would be too, if I thought if what they are doing yielded a big increase in security.
The OS should be so secure loading any app, signed or not, malicious or not, is mostly harmless. That is true for iOS and Android. You can always uninstall an app, and you have to give it additional permissions to access your data. I don't know if an app can attest it was downloaded from the web store so organisations like banks can be sure they are talking so software they issued. If it isn't, that's a security hole that should be closed.
Unlike adding attestation, sideloading apps doesn't look to be a security hole that needs fixing to me. I'm doubt it provides much additional security. I've personally had to fix phones whose apps went rogue after a spammers bought the developer licence from an abandoned app. Worse, the app still had the permissions granted to the original.
This new requirement does create barriers. I use apps from F-Droid. They typically have no ads, and they do what they say on the box. Security in the long term is higher than a Google store app because the source is available, and F-Droid uses reproducible builds. But I would not be surprised to find some open source app developers that aren't as keen as you are to hand over their private data to Google in order to get their keys signed, so there will be less F-Droid apps. If that happens, this new requirement would lead to a net reduction in security for me.