Having the same problem on a Mac m4 Pro. No Firewall, no antivirus…
Internet working fine - reinstalled the launcher several times, restarted the Mac several times. The funny part is, that randomly it works and if I start the launcher an hour later the error message pops up again. At the same time the launcher is working on three other Windows-PC and on my iMac.
I couldn’t figure out what causes the problem. Now I am using the Prism Launcher and it not only works fine but you also can configure different modded versions also…