Without attestation, banking apps stop working and without a banking app, you are locked out of modern life in many ways.
This latest Google move makes it impossible to run an attested Android without the sideloading limitation. That means that you'll have to choose between GrapheneOS and using your banking app.
I'm sad to say that I've already had to make that choice :-(. I feel that I was coerced into it.
Then bank apps themselves started giving me warnings that my device was insecure (the irony) and I got increasingly frequent KYC questionnaires coming my way. One of the banks also disabled access to some money transfer services, which I suspect is because of some flag on my account in their system.
I had to ditch GrapheneOS at that point. There are simply no banks that I can switch to.