We'll have an initial beta of Node-RED 4.0 in the next couple weeks.
We already publish docker images for Node-RED 3.x for node 18, all the details of the available images is available here: GitHub - node-red/node-red-docker: Repository for all things Node-RED and Docker related
There's nothing stopping you upgrading today.
The latest tag does still point at node 14, but as has been discussed a number of times, changing the latest tag to a different node version is a major change and not one we will do in a minor release.
