Is there any way to add those tags on a movie through mp3tag, and can I add subtitles?

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There is a field called SUBTITLE but I doubt that you mean that.
Otherwise I think that most of the attributes that you showed are properties of the audio part. And MP3tag does not manipulate the audio part.

I think that 4K, R rating, Subtitles aren't quite the audio properties as they are in charge of the picture, but tho is there any other way can add subtitles to a movie?

I assume, the "R" is a rating category meaning "Restricted" or "Contains some adult material. Parents are urged to learn more about the film before taking their young children with them."
This R rating is only valid for USA. You can compare the various ratings in a nice overview for other countries.
CC refers to "Closed Captioning"
AD refers to "Audio Description"

Why would you save such informations into a movie as metadata if you can read them* anytime from the movie file itself with tools like ffmpeg? I don't believe that you will find many players capable to read such informations from metadata anyway.
*only exception: the country rating

And subtitles itself should be added as separate files with the same name as the movie file. Most common file types are *.sub and *.srt

I know, I've just showed the example, the question is: How do I display those ratings, subtitle and other on a downloaded movie. And btw I have subtitles the same name as the movie and in one directory but can't add them to Itunes

Most likely also related to this topic:

To have iTunes recognize the subtitles you have to put (mux) them in the video file.
A program like My MP4Box GUI can do that.
And rating can come from iTunEXTC tag.

What value should I add to display age rating in iTunes? I've added "mpaa|PG-13|300|" (wasn't working) then changed to "mpaa@PG-13@300@" (wasn't working either)

I'm not sure atm what the correct syntax for the field is, but it could be another problem.
When you edit this field in the Extended Tags, Mp3tag writes the field name in capitals.
But for iTunes to recognize it needes this exact notation iTunEXTC

So for the moment you should edit this field in the columns (or tag panel, but it needs a different fix) . You can create a new column with field and value %iTunEXTC%

I'm sorry, but how do I edit that field in the COLUMNS?

Right click on a column header and choose "Customize columns". There you can add a new column for that tag field.

Rating can't be applied either