For our RKE2 cluster created in rancher, each node shows label "plan.upgrade.cattle.io/system-agent-upgrader=c1d7..." in gui. What is this? Is it normal?

It's a SUC plan to upgrade the rancher-system-agent service on the node. Yes, it's normal. Is there a problem?

Thank you for the reply. There are many node labels that are not shown in the UI, this is. I worried it could be a sign that there is a problem with the cluster/node. If it's normal, then no problem. It would be nice if (interface-) elements like this that are not standard kubernetes were mentioned in rancher / RKE2 documentation. I haven't been able to find anything.

We don’t document every label or annotation you might find on some object, it is mostly considered an implementation detail. In general if you see that it says

<http://cattle.io|cattle.io>

it is from rancher and you should not mess with it.

I agree. This is the only label that is shown in the rancher UI after creating a "default-everything" RKE2 cluster, though. More of a rancher ui issue I guess.