Running nodetool upgradesstables after version upgrade

After an upgrade from 4.6 to 5.0, do we need to run the nodetool upgradesstables ?

The short answer is no.
The long answer is: even if a new ScyllaDB version introduces a new sstable version, you don’t have to manually upgrade sstables via nodetool upgradesstables ,this will happen automatically as the sstables are compacted, and in general new sstables are written in the new version.
Gradually all sstables are migrated to the new version. This might take some time, but this is fine. There is no rush to get all sstables to the same version.