Is there a way to temporarily disable the jailbreak, then open/use the banking app, then re-enable jailbreak? Even if it required a reboot I'd be okay with it.
The short answer is sometimes yes sometimes no. Some jailbreaking detection works by attempting things that wouldn't succeed on a non-jailbroken device and some detection works by looking for signs of specific jailbreaks. It's a real cat-and-mouse game.
unc0ver isn't one, but a "rootless" jailbreak is usually undetectable. This one hasn't been updated with iOS 13 support but was popular for iOS 12: https://pangu8.com/jailbreak/rootless-jb/
I haven't used it myself, but two very similar kernel-level jailbreak detection bypasses were just released for unc0ver 13.x, FlyJB and KernBypass: https://github.com/akusio/KernBypass-Public
A couple of my banking apps detect my jailbreak but allow me to continue after hitting "Okay". The only app I ever wanted to use that refused to let me in was the Nintendo Switch Online app. Steam works fine. If you don't play games on your phone it isn't really a big deal imo.