Add guest account to a channel without adding them to the teams

Gedion000 Unfortunately, there isn't an easy way to do this with Guest accounts. For standard and private channels, your guest will need to be part of the team first. Guests will be able to see the General channel and any other standard channels.

It's not a great solution, but you could have a team where every channel is Private and only the General channel is standard. Or you have a team set up just for those guests.

Another option would be to move your collaboration to an external chat - again, not ideal and fairly limited.

One more option would be to look at Shared channels. However, this requires additional permissions to be set up with your admin and your guest's admin: Guests and shared channels in Microsoft Teams - Microsoft Support.  If you can get it set up, Shared Channels are a great experience where your guest can continue using their regular work account without having to switch to their guest account on your tenant.