SharePoint Online and indeed, M365 as a whole, doesn't really conform or implement the old fashioned style of multiple environments for GxP type dev/QA/prod activities.
I feel there is some benefit to having a very small tenant which allows you to test global-level settings (i.e. implementing Azure B2B Preview for SPO), but other than that, everything is content in SPO. Having separate site collections for specific activities, such as building SPFx webparts, is not a bad idea (don't forget developer tenants can be had for free and are created on a per-user basis).
Other content-level changes, such as documents, pages, etc. can rely on the versioning system built into the platform.
You may want to have your quality team review https://learn.microsoft.com/en-us/microsoft-365/compliance/offering-gxp?view=o365-worldwide.