Mac stuck on a white screen after the Apple logo

If it happened right after a macOS update, give it a good while before forcing it off. Some updates sit on that screen for 30+ minutes and pulling the plug mid-way is what actually breaks things. On an Intel Mac also try an NVRAM reset before reinstalling: power on and hold Option+Command+P+R for about 20 seconds. Apple silicon Macs don't need that, they reset it themselves.

Unplug everything first, external drives, docks, monitors, even the USB hub. A bad external device can hang startup right after the logo and it's the easiest thing to rule out. Then try Safe Mode. On an Apple silicon Mac, shut down, hold the power button until you see startup options, pick your disk, hold Shift and click Continue in Safe Mode. On an Intel Mac, power on and hold Shift straight away. If it boots in safe mode, restart normally once, that alone clears caches and fixes it surprisingly often. If it won't get that far, go into Recovery (same power-button trick on Apple silicon, Command+R on Intel) and run Disk Utility > First Aid on the startup disk. Still stuck after that, Reinstall macOS from the same Recovery menu. It puts the system back without wiping your files, though if you have a backup make sure it's current before you do it.