Ctrl-+ works for me on Firefox and Opera, but not Brave. This article, dated a few days ago, seems to indicate that font changing is not yet implemented:
I have a huge monitor and glasses optimized for the appropriate distance; so tiny text is not a big problem for me. What is a problem is the hardwired seriph font. With characters only a few pixels wide, the seriphs are distracting clutter.
Try using ctrl-= on your keyboard rather than your 10-key. I tried the 10-key first, and it didnt work.