I’ve just tested with the same command and it works fine.
Try specifying the name of the Database Server and the Content Database in the command and try again:
Restore-SpSite “http://mydevsitecollectionpath/” -Path "D:\pathname\12102020.bak" -Force -DatabaseServer <SQL> -DatabaseName <DB>
Reference: Restore-SpSite : The operation that ...
Please refer following powershell to get all site collection owners for each site collection in SharePoint farm:(Change the file location for yourself)
#Set file location for saving information. We'll create a tab separated file.
$FileLocation = "C:\Temp\SiteCollectionOwnersReport.csv"
#Load SharePoint snap-in