To rollback f/w, look here, https://kb.netgear.com/23960/How-do-I-manually-upgrade-firmware-to-my-NETGEAR-router. Follow the steps. Once you get to the SUPPORT page for the router check the available ones vs. your f/w. Have the latest, then press the 'down arrow' to see older one.
I suspect you have different problems though. Not sure what, but "my 5GHz is showing but we can’t connect to it" could be a sign of something else going on. Interference, device problems, etc.
Yes, buffering is usually h/w, but it could be your modem as well. Some modems that are Puma6 chips have Buffer Bloat as well that can slow you down.
Your ISP speed might be too slow to do what you want (unspecified as well) when you get the buffering? If you recently updated the f/w and then started seeing the buffering it could be the f/w, but you didn't state that either?