No ur not VAC banned, I checked. If you have issues with VAC it would give you a message when joining a server.
I guess you crash out to windows? Or is it just the loading that jump back to menu?
I searched a bit on the net and ALOT! of ppl seems to have this problem many of them uses mac for some reason¿
But on the new maps atleast and maybe even on the older ones I personally heard many complain about lag, and low fps. And I drop down to 70fps sometimes and my PC shouldnt do that.
I tested TF2 at 4K around an average of 150fps but I mainly play at 1080p. So Valve have done something really bad on this update.
And its too bad that not everyone can play this update, kinda kills the game for those players.
But just for fun, try and lower the res for example to 1080p to 720p and see if you can join. Could be a stupid thing that checks ur FPS while loading
and if you are below a certain FPS number when loading you might not connect. I wouldnt be surprised, Valve never surprise me anymore so.
And yes its a longshot but couldnt hurt to try.
Also check this thread you might find your solution here.
https://steamcommunity.com/app/440/discussions/0/530646080850796989/There are some explanations that some even crash from new gun textures cause the code is broken for it so GG TF:Go
Other than that, check ur printer cable.