I'm a newbie game developer, but I've been a fan of open source and a linux user since the 90s.
It's definitely possible to make a game using only open source - I think the limitations are your skill level and the amount of work you want to put in, and of course a learning curve which should be expected whenever trying any new tools.
All of the projects on my itch page are made using 100% open source tools. I'm still very new and inexperienced; I don't have any training or education in any tech field: I'm just a hobbyist, but you can see what progress I've made since July of this year.