Generating report on SharePoint Online Site collection is easy, you can run the below command to export the report.
Connect to SharePoint Online Management PowerShell and run the below command
Get-SPOSite -Limit All | export-csv C:\Temp\SPOsite.csv -NoTypeInformation
Output will be like below and you can filter based on your requirement
All the information about the Site collections in your tenant will be available in the output.