Received a check from irs with memo “tax return” months after taxes filed and return refunded

This appears to be a scam.  The IRS does not issue tax returns.  They issue tax refunds.  If you were not expecting this check, call the IRS and see if they really sent it.

Sometimes scanners send a bogus check in order for you to deposit it and then they can obtain your banking information.

Please don't deposit the check until you verify with the IRS that it is legitimate.

If the check is from the US Treasury and not a large amount, then more than likely it is for  interest paid on your refund if the refund was delayed more than 45 days.

Did you have any unemployment?  If you filed early before the 10,200 unemployment exclusion the IRS recalculated your return.

Check each line on your return.  Maybe you entered some withholding or estimates wrong.  

Or it could be the 3rd Stimulus payment?  How much is it?  And the check would not say "tax return" on it.  It would say like Treas and maybe interest and the year it's for.