@mkretzer it's worth noting that the feature you are asking about possibly being added to Veeam v10 would more usefully be requested of Microsoft as a possible enhancement to the ReFS engine. Like @foggy mentioned, it's analgous to a volume that has Data Depulication enabled, where copy/move actions to other volumes will trigger 'rehydration' of de-duplicated data. Solutions to this are
1. Start a new backup chain, as original poster has opted for in this scenario.
2. Assuming sufficient available storage ( and IOPS capacity plus CPU time) on the new volume, copy the data from old volume to new volume and allow the rehydrated data to go through deduplication again.
Neither of these are pain-free scenarios, but thats why we pay careful attention when we do our capacity-planning work to avoid having to do too many storage-platform rip & replace operations, right?