This (over 3 forums) is the 6th similar thread I have seen recently.
When the bearings in the freehub itself get knackered they tend to bind up. Off the bike they work fine, on the bike they don’t, that little side load kills them.
It is a quick and easy job if you have sockets, hammer, the bearings and some wood blocks.
Pull off freehub body and you can check bearing sizes (can’t remember off the top of my head). Then is a case of knocking them out, fit new ones (make sure socket only touches the outer) making sure the spacer between bearings is fitted, and any end spacer you may have (mine doesn’t only the end cap).
Whilst off you can also clean out the pawls and regrease. DT specify a particular grease, I did an emergency fit before I went on holiday 18 months ago and used a tiny amount of machine grease with no issues. Just make sure the spring clip goes back on in the right place and doesn’t get bent.