My understanding of "mesh" is that it is using dedicated radios for connecting to the next access point. This is as opposed to a "extender" where it uses the one radio which keeps swapping between providing client access and connecting to the next access point - hence reducing bandwidth.

I know with Ubiquiti the mesh APs can be used as regular APs - which is not surprising as their APs do POE. Google's AP are the same, except for the POE part. For what you want to do the AP in the garage would not need to be replaced, but by going with something like Ubiquiti or Synology everywhere you gain a single point of management.

I've gone full Ubiquiti and I'm happy with it. I started with just a single AP to add AC to my existing router whose wifi I disabled. Later, when we moved to a very non-American house build with three layers of red brick, I added two additional APs, switch for POE, and router (USG3). At about $500 total it was not cheap, but it has been boringly rock solid.