Spacebar doesn't work sometimes in Safari

Quite often, while I use Safari to enter texts, the spacebar doesn't work (no response when the spacebar is pressed, but a blue rectangle shows up randomly). But it works with other apps like Notes, or Text. For not any particular reason, it works again after a while. Need some help to identify what is wrong in my computer or operation.

Current system:

Mac mini M1 2020, Monterey 12.3.1

Apple bluetooth keyboard (first generation) and mouse (2nd generation)

Thanks.