Perhaps drawpile: https://drawpile.net/ https://drawpile.net/ is worth a look. I have seen people create rather large artworks with it, you even have support fo

Perhaps drawpile: https://drawpile.net/ https://drawpile.net/ is worth a look. I have seen people create rather large artworks with it, you even have support for pressure sensitivity. It does not run on tablets though as there is only a desktop version.