I am signed in on minecraft, but whenever I open the launcher it logs me out and I can't log back in again because the sign-in portal is blocked by my network. I can play the game when I turn my internet off (it doesn't sign me out that way), but once signed out I cannot login and play offline. Is there any way I can get around this?
It sounds like your best bet would be to use a VPN. It would allow you to be accessing a different network virtually and it should let you get around this issue. Or as you mentioned you can just play it solo offline. Networks often times at schools and/or workplace environments will have these network restrictions that basically blows network traffic or access to certain types of content, in this case it would be games.