Sophos do provide an official Uninstall/Remove tool for uninstalling Sophos EndPoint on a Mac.
This used to work fine on Macs but with macOS Big Sur (and Monterey) Apple have again moved the goal posts and this results in the System Extensions being left behind and still active.
For Big Sur and Monterey there are now three possible solutions.
Clearly option 3 looks more suitable for an Enterprise environment.
Unfortunately, option 3 not only needs a very recent version of macOS but it also requires the developer of the system extensions - in this case obviously Sophos to write support for this new capability in to their own built-in uninstaller. I strongly suspect Sophos have not yet done this.
The following two articles provide excellent background to these issues - which I have seen discussed in the Big Sur EAP forum but to which I cannot post.
The second link above also has links to some of the official Apple developer documentation on how to implement this function in the developers uninstaller. Sophos therefore should look at those links as well.
It should be noted that apparently Microsoft have added this capability to their own Microsoft Defender uninstaller.
Thank you for reaching out to the Sophos Community.
I have relayed this information to our internal teams. I will follow up on this thread as more information on future development becomes available.