Most of my playtests were also done online. I built a Windows desktop version of the game and sent it to friends, and they streamed themselves playing it over discord.
I also think you can publish the game to twitch in such a way that only certain accounts can access the game - that way you can have it be online without actually submitting it for the jam.
But I also saw a lot of people submitted their games early, and kept updating them before the deadline.