Deploying Plone 6.x using Docker Images plone-frontend and plone-backend having trouble with :null:3000 part in the URL

There are at least three posts on this forum that discuss a similar issue. Did you see these:

https://community.plone.org/t/issue-with-deploying-plone-6-on-plesk-server

Apparently, you should include RAZZLE_PROXY_REWRITE_TARGET in your docker configuration. Documented here: How to use environment variables — Plone Documentation v6