You can just say no. You are not obligated to say why. It's not like the recruiter is going to be able to do anything about it. Even if they passed that message

You can just say no. You are not obligated to say why. It's not like the recruiter is going to be able to do anything about it. Even if they passed that message up it's not like they anyone going to be like "OMG, dijit declined our offer because of Teams, we better change that ASAP". I hate Teams also but honestly if you are hung up on this, I wouldn't want to hire you anyway.