My tests suite broke on 3.20 because of the "TTL index" error and tested now using mongomock.ignore_feature("TTL index") and this LGTM, also I think it will bring high flexibility for the future of mongomock. Would you considerer publishing in pypi after merging?

Just to mention that as of Oct 19 the latest tag (3.20) does not have this patch. Looking forward to have it released in PiP as I'm forced to stick to 3.19 until then.