I keep getting a weekly activity report for someone I don't know

I don't know how to block them. I get an email that is sent to a variation on my email address (missing the . in a gmail address), so I assume it was an accident when setting up the report. It's a weekly email. The email I get doesn't seem to have an unsubscribe
link that I can see.

I would say check your Family account page
(details here.) See if there are other accounts you don't recognize in your account family? Or do you know if your account is listed as an alias on another MS Account?

Blocking the other player should ensure that you do not see any items in your feed from him.

Just try and flag that as spam it is likely that the person may have made a mistake on their side somehow; they would have to fix it. I get other people messages all the time in my gmail as I have had the account for a very long time and people try creating
variations that other email server screw up when forwarding it.

I only see my laptop under devices. Maybe you're right somebody accidentally used my email as an alias. I tried replying to the other email address in the weekly report, but heard nothing back.