I try to start minecraft in the launcher but I get the error "Skipping bad option: lastServer:"
if you want the game log:

16:42:32 launcher Preparing to launch minecraft client for 1.12.1
16:42:33 launcher Checking installations.
16:42:33 launcher Minecraft client 1.12.1 is ready to start.
16:42:33 launcher Starting!
16:42:33 launcher Using default game log configuration client-1.12.xml (outputs XML)
16:42:34 bib Setting user: SirLotsaLocks
16:42:37 bid Skipping bad option: lastServer:

thats it. this is on all minecraft versions for me. I can't find a fix either.