About %51 attack. If you have hashrate higher then %50 then you can manipulate some part of the blocks. However against old days full nodes (economicly good ones) in general dont do mining. So mining and nodes are seperate entities.
Bitcoin nodes (full nodes, pruned nodes) have never worked through mining Bitcoin blocks and confirming Bitcoin transactions. Never, it is first big and important thing you must know about Bitcoin nodes.
What is a Bitcoin node?Bitcoin node's roles on Bitcoin network.About Bitcoin network.About Bitcoin network 51% attack, you can read there with many information and clarification, I don't think I need to rewrite it in this post.
How many Bitcoin confirmations is enough?