[SOLVED] Changed Permission, Can't regain access

I am using Sabaayon, recently updated.

I have several partitions with different distros, and 2 partitions with just Data.

I have my root & my swap partitions on fstab, and when I need access to others I mount them manually or by clicking them on Thunar.

When I have to move files from my root partition to one of the data partitions I have always used command line with root privillege in Sabayon.

Have done so for many years, being too lazy to understand all the finesses of permission granting.

I search the net when i have a special reason. But I don master the whole logi of permissions.

Today having some complex work to do I decided to finally experiment with trying to set permissions to move files via Thunar.

Read several texts I found in my searchs and they said just about the same, which I tried to follow.

The folders I wanted to use are in the data partition labelled DataFrugal, which was owned by root, belonging to group root.

After I did
chown -R root:arthur /run/media/arthur/DataFrugal/Dokuments
chown -R root:arthur /run/media/arthur/DataFrugal/
chown -R arthur:arthur /run/media/arthur/DataFrugal
chown -R arthur:arthur /run/media/arthur/DataFrugal/Dokuments
chown -R root:root /run/media/arthur/DataFrugal/
trying chmod at every step above with different values (755,766,774),
I noticed that Thunar was from my first modification unable to read the documents in the folder "/run/media/arthur/DataFrugal/Dokuments".

Folders in "/run/media/arthur/DataFrugal" were listed as O bytes and showed nothing when opened in Thunar. They also elicited a "no permission" message from terminal as user (arthur)

As a mattter of fact the same was true for all folders in that partition.

And the icon for folder "/run/media/arthur/DataFrugal/Dokuments" changed from a folder icon to a document-like ikon, upon changes. But changed back to a folder icon if i closed Thnuar and rhen re-started it.

But I could find the files as root in the terminal.

What is puzzling me though i s that now when I do:
less /run/media/arthur/DataFrugal/Dokuments
I get:

totalt 84
drwxrwxr-- 13 root root 4096 10 dec 20.27 ./
drwxr-x---+ 6 root root 120 10 dec 22.39 ../
-rwxrwxr-- 1 root root 8366 15 nov 15.40 arch_usb128_copy_grub.cfg*
-rwxrwxr-- 1 root root 8366 15 nov 15.29 arch_usb128_copy_grub.txt*
drwxrwxr-- 5 root root 4096 9 dec 21.54 Bilder/
drwxrwxr-- 13 arthur arthur 4096 10 dec 19.52 Dokuments/
drwxrwxr-- 2 root root 4096 13 nov 22.40 Hamtningar/
drwxrwxr-- 4 root root 4096 10 dec 20.28 ISO/
drwxrwxr-- 2 root root 16384 29 aug 14.53 lost+found/
drwxrwxr-- 2 root root 4096 31 okt 16.09 Lankar/
drwxrwxr-- 6 root root 4096 6 dec 20.53 Musik/
drwxrwxr-- 4 root root 4096 13 nov 22.49 Software/
drwxrwxr-- 2 root root 4096 6 sep 23.40 Spraaket_i_Mittens_Riket/
drwxrwxr-- 4 root root 4096 21 sep 14.00 .Trash-0/
drwxrwxr-- 14 root root 4096 1 okt 16.57 Viva_o_Slackware/

And here is a sampling of the listing for the folder "Dokuments":
totalt 28648
drwxrwxr-- 13 arthur arthur 4096 10 dec 19.52 ./
drwxrwxr-- 13 root root 4096 10 dec 20.27 ../
drwxrwxr-- 2 arthur arthur 4096 10 dec 19.52 Aninha/
-rwxrwxr-- 1 arthur arthur 33178 25 sep 21.35 Apple MacBook Pro 13- inch (mid 2010) - Gentoo Wiki.html
-rwxrwxr-- 1 arthur arthur 7752 7 aug 19.08 CERTIFICATE*
drwxrwxr-- 2 arthur arthur 4096 9 dec 19.22 Dokument/
drwxrwxr-- 4 arthur arthur 4096 6 okt 15.11 Downloads/
-rwxrwxr-- 1 arthur arthur 1219 1 sep 14.52 grub.cfg.bak*
-rwxrwxr-- 1 arthur arthur 39523 3 okt 15.53 InstallArchLinux2020.odt*
-rwxrwxr-- 1 arthur arthur 46938 25 sep 21.22 Install the Latest Nvidia Linux Driver - LinuxConfig.org.html*
-rwxrwxr-- 1 arthur arthur 27806431 6 sep 11.12 kinapodden_i_p1_premiar_for_kinapodden_i_p1_20200820_1209203325.mp3
drwxrwxr-- 2 arthur arthur 4096 21 sep 14.01 Laenkar/
-rwxrwxr-- 1 arthur arthur 98778 25 sep 21.33 MacBook Pro 7,1 (nVidia based); Dual boot.html*
drwxrwxr-- 5 arthur arthur 4096 12 nov 09.52 macbook_stuff/

BUT as one may check at the enclosed .jpgs, files and folders that are listed as having owner arthur and group arthur in the terminal are presented as having owner root and group root in Thunar.

I am lost. Can anyone help me ?
Attached Thumbnails