After chatting with support, it looks like Retool (currently) hosts in Azure us-west-2 ( Washington).
Note: Couldn't find this information in docs or community so this may be duplicate information.
I just found out from support that the backup is in us-east-1 (N. Virginia).
Thank you so much for documenting this, @erichosick! Will sync with our docs team on making this even more visible.