does not respect the selection and moves when pasting

You can alternatively use the Apply Image command to "stamp" a source channel onto a target channel, with the added benefit that it does not use clipboard or move.

Copying content from one channel and using Paste in Place on another channel is working for me with Photoshop 22.5 on Windows 10.

If what you paste isn't aligning properly, you could try instead to copy all of the contents from the one channel, paste it into the other channel, and delete what you don't need.