Bicycles to EU after Brexit - ATA Carnet

Picked up on the guys going over to Spain for a charity bicycle event and the fact they were clobbered for duty.  Seems the bikes were transported in a van while most passengers went separately. Assume they didn't get an ATA Carnet to cover the bikes as post Brexit (benefits of being a 3rd country!!!) a Carnet is now needed when transporting goods on trailers or in vans - in this case their personal bikes which were not identified as the specific means of transport to cross the border.  I have tried to find the ruling for family bikes when travelling inside cars+caravans & motorhomes across to the EU and have failed apart from a second-hand mention of a requirement to take proof of ownership for each bike over 300 euros.  Having read another piece, it also seems e-bikes may be in a different category to pedal bikes and may, as a powered bike, be lumped together with motorbikes and thus require a Carnet where necessary (in a motorhome garage?). Can anyone out there shed any light?