If you are not using OpenStreetMap tiles or they come from other source than tile.openstreetmap.org, then it is not applicable to you. As in such case you are not using OpenStreetMap Foundation tile servers.

https://operations.osmfoundation.org/policies/tiles/ requires and required for long time to provide referer but it was not enforced.

Now It is visible as some map tiles being replaced by

> Access blocked > Referer is required by tile usage policy of OpenStreetMap's volunteer-run servers: osm.wiki/Blocked

message.

Currently it is a brownout with only some tiles failing but error rate will go up.

This block is automatically enforced and can be fixed by providing referer header as required by rules.

Apparently quite a lot of sites are affected by it, with some people being confused by why they get this error. Note that if you open file:// in browser then referer header is not send, and there is no known way to fix this problem.