% of full nodes running Bitcoin Core versus other node software
bitnodes.io, in its user agents chart, show an &quot;Other&quot; category, but probably it will include also older versions of Bitcoin Core.

On blockchair.com you can find details of which clients are used by full nodes, but they are grouped by user agents, so you need to manually count Bitcoin Core version and other clients.
on coin.dance you find exactly what you looking for, but right now is in maintenance, here there is a snapshot from archive.org: https://web.archive.org/web/20210124183839/https://coin.dance/nodes