Is there still not a placeholder for folder total files?

I would like to create an action where "total tracks" are automatically filled with the number of files in the folder without using "%_total_files%" because that puts the number of files I'm working on. With a placeholder for how many files the folder contains, I could load multiple files from multiple folders. Is there any way I could do this?

Yes.
Either drag and drop the folders you want to load from the explorer or use the "Add folder" function

Just a side note: Not all files that you see in MP3tag represent the files in a folder.
A folder could also contain files that MP3tag does not support.
Also, a filter could show fewer files of a folder than are actually present.
But as you do not tell us what your use-case is, it is a little hard to tell you whether there is

I already know I can load multiple files from multiple folders.. My question was, is there a placeholder for how many files a folder contains? It would be very convenient for me.

You can find all available placeholders in the documentation:

No. There is no placeholder to show this property.

I use a simple method to fill the tracktotal field.

  1. Open all music files of all those libraries in Mp3tag. Sort them by %_path%. Select them all.
  2. Click Auto-numbering Wizard. Select checkboxes: Save total count of tracks + Reset counter for each directory. Click: OK.
  3. Run the Action Group below. (First place it in your %appdata%\Mp3tag\data\actions\ folder.)

Spelling corrections#Track number#Delete leading 0 + get tracktotal.mta (293 Bytes)

(I searched for this. Although it is a simple solution, no one has yet explained it in detail. There always are beginners.)

It may be worthwhile to first save the original data from the TRACK field in a user-defined field to restore that data e.g. if the computed totals do not match the totals in a particular album.

Also, I would like to point out that any attempt to use PATH or similar properties to see "files in a folder" only shows the files handled by MP3tag. You don't see all the other files like txt, jpg, png, lrc etc.

I only use it for, what JPMusic wants:

In this case, I think, neither is necessary. Only the music files need to be counted. But, of course, the Action Group can be supplemented according to individual needs.

Ohh... But yes, in the Settings >> Tags >> Restrict incoming files to only music files, excluding even cuesheets. It never occurred to me, that anyone would want to open other files in Mp3tag.