I played on 720p/60fps on a lan where I only brought my laptop. 720p and even below is super playable if you're already used to fucky configs. it's not ideal, but better low res than low fps
I will also say that you don't have to be a ""cooperate slave"" to slowly save up 400-500 bucks to get a gently used optiplex + used graphics card + mediocre 144hz display. that's like 3 weeks part time minimum wage job, and most retail jobs are paying a decent bit over that right now.
TF2 isn't the most optimized title ever, but we are talking about a 14 year old game at this point... I understand that for some, this is a privileged thing to say, but it seems like you are just choosing not to work towards a solution, so I don't feel so bad ¯\_(ツ)_/¯