[JamieD]

Didn’t they change the rules last year to allow pre-recorded vocals in the backing tracks?

This is correct. Since 2021 pre-recorded backing vocals are now allowed, though the lead vocals must still be performed live. This was brought in under the pretence of reasons due to COVID to allow delegations to bring fewer people, but in reality, it is here to stay for the long haul. 

Personally, although some authenticity is lost in it being a "live performance" it sounds all the better for it, especially in pop songs where live BVs can often sound awful.