Core uses Node 14.x at the moment, the oldest LTS line of Node, being EOL in April 2023.
This line is in maintenance only mode since October '21.

I filed https://github.com/jenkinsci/jenkins/pull/6754 to move forward from 14.x to 16.x, the active LTS line. Given the time I filed this PR, we're almost moving from one maintenance line to another. 16.x will be the maintenance line in October '22 and being EOL in September '23.

Node 18.x is the current/latest line, which will be the next LTS line superseding 14.x's active time until October.
Switching to 18.x allows us to benefit from active development for a bit longer than just a few months. 18.x's will be the maintenance line in October '23 and EOL in April '25.