Standard is 5 panels per page max for folks who do professional comic lettering, that way they have room to fit bubbles, speech, and sound effects.
But in the world of online indi stuff, you can squeeze more if you're doing it all yourself, as long as you have room for your speech n it's not crammed. The reason is because we who do digital n never do print, don't need to worry about actual page sizes for print, so you're not limited on format. So all that's needed is to not squish bubbles n text. c: