Bluetooth accessories won’t connect since update 15.3

Have you restarted the device since the update? You might also try a Forced Restart, no guarantee but worth a try...

https://support.apple.com/guide/ipad/force-restart-ipad-ipad9955c007/ipados

Same issue. Turned phone off, back on, did a hard restart, did a network restart, nothing works. Doesn’t even see device - but husbands phone (different model - different software level) connects fine.