Is it a mistake to try to update while doing other things and running lots of different VMs, includong some that may be being updated?
The only risk is one qube failing to update because you don’t have enough RAM. In which case you just have to repeat that qube’s update.
You’ll only have to restart all your qubes that received an update afterwards. You can see which ones in the domains widget (top-right). They’ll have a style icon.
It might also slow down your machine, which might be inconvenient for you while you’re using it. Also, remember to restart all running qubes afterward so that the updates can take effect.