On Spring Boot 3 besides exception, method, outcome, status and uri, the error tag is also being generated:

http_server_requests_count{error="none" ... }

This tag is not on official docs neither ServerHttpObservationDocumentation class and overlaps with exception tag.
Looking at the code it seems that this behavior is added by micrometer's DefaultMeterObservationHandler which is configured by ObservationAutoConfiguration.

A possible quick-fix would be to override DefaultMeterObservationHandler#createErrorTags to return Tags.empty().

On a side note, an additional undocumented behavior added by DefaultMeterObservationHandler is the http.server.requests.active metrics. Should this be documented ?