The fix for quickstep crashing issue since Android 15 is already out.
The delay due to FairPhone update country rollout and each operator makes that update may take some days to weeks to reach your Fairphone.
It didn’t reach mine for now.
Maybe the issue described in this thread is related to the quickstep one.
For the time being, for a “turnaround in the meantime”, I use fossify launcher from f-droid, simple, light, very similar to quickstep, maybe I’ll keep it after the update anyway.