Batch renaming by mistake should be reversible - why isn't it?

On the topics-

"When a group of files is selected, and one clicks just one of them, it should automatically de-select the rest"

It is important to note the exact location of the cursor where you 'click'!

If you click on the IMAGE area of a photo, then this photo becomes the 'Most Selected / Active photo' of all the selected photos. (it has the brightest border.)

If you click on the grey BORDER of one photo, then this photo becomes the only one photo selected. All others are de-selected.

Helpful to remember is the shortcut [Ctrl+D] to De-select all images, before clicking anywhere on one photo to select it only.

individually named to identify the rooms.

My suggestion would be to- NOT rename the original files!

Instead give each photo a 'Title' or a 'Caption' in the metadata that is descriptive of the "rooms". Because in the Export dialog you can create exported files with names that include Original filename, Titles, Captions, Sequence, etc, etc, or any defined rename template you desire. (eg. Title_Original Filename)

If you need to get the files back to the filenames written by the camera, Lightroom Classic already keeps that around as the Preserved Filename (can be seen for renamed files in the Metadata Panel, depending on which fields are visible). You can use the Preserved Filename rename token to revert multiple selected files back to that camera filename. That isn’t a straight undo, but it’s a big help if you need those camera filenames.

I have been careful to say “camera filenames” and not “original filenames,” because there is an Original Filename token but it doesn’t really mean the original camera filenames. It means the current filename, which in your case is the wrong one.

If you have a formal feature request that can be publicly tracked/voted on, with possible comment from actual Adobe product managers, those happen at the official Lightroom Feedback site.