$ sudo umount /dev/sdb1
/dev/sdb1: recovering journal
/dev/sdb1 contains a file system with errors, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Invalid inode number for '.' in directory inode 112197682.
Fix<y>? yes
Pass 3: Checking directory connectivity
'..' in /.Trash-1000/files/[file names]), should be /.Trash-1000/files/[file names].
Fix<y>? yes
/lost+found not found.  Create<y>? yes
Pass 4: Checking reference counts

Pressed y to all q's

/dev/sdb1: ***** FILE SYSTEM WAS MODIFIED *****

Read & Write restored 🙏
The new lost+found folder contains files that i had moved to Trash.
There's a new .Trash-1000 folder that contains .trashinfo file in the info folder. When i delete the file it replicates and adds a .trashinfo extension. I'll let it be.

Permissions problem was easier to fix than it looked, thank you for your help!

Check dmesg output and syslog for messages about the device or the mountpoint.

Try e2fsck -n <device> (-n means read only so should work for mounted devices). If that shows errors you need to *umount* the device, then run e2fsck <device> (specify the device, not the mountpoint).

First check the output of mount to see whether this applies at all. (sticking to /dev/sdb1 as example)

$ mount
$ sudo mount -o remount,rw /dev/sdb1

Open question to answer is still: Why was the partiton mounted read-only at all?
Re-mounting the partition rw manually is curing a sympotom - if the real reason allows this at all.

Any time I've used fsck, I've done it on an unmounted device, like /dev/sdb1 for example. I just tried running it on a mounted filesystem, using the directory, and I got the same error you got about superblock.

Yes, i replaced <user> and  <UUID> with the correct names, i double-checked with # blkid and # lsblk.

In Gparted i formatted the new WD Elements drive as ext4. I don't remember enabling the msftdata flag. Disabling the flag isn't possible, the key icon in the Partition column probably indicates the drive is locked. I can open files, copying files to the drive and editing isn't possible.

I have no clue how this switch could have happened. Just format the thing?

Thanks.

Maybe you show us with the drive connected:

# blkid
# lsblk

Then: the unallocated space is fine. But why does the ext4 file system have a msftdata flag, a Windows descriptor?

# fsck /media/<user>/<UUID>

Returns error message:
fsck.ext2: Is a directory while trying to open /media/<user>/<UUID>

The superblock could not be read or does not describe a valid ext2/ext3/ext4

Commands:

# e2fsck -b 8193 <device> 

# e2fsck -b 32768 <device>

Error message:
e2fsck: Is a directory while trying to open /media/<user>/<UUID>

Gparted shows 2 partitions:
1. File system ext4
Flags: msftdata
2. File system 1 mb unallocated
No flags

Are these settings ok for a media drive?

su #become root, alternatively sudo su
fsck /media/<user>/<UUID> #check the file system for errors and repair if required
chown <user> /media/<user>/<UUID> #make sure the directory is owned by the user
chmod 777 /media/<user>/<UUID> #set permissions for the directory for general access

HTH!

$ sudo chmod g+w /media/user/UUID

and reboot doesn't fix it.
Reformatting the drive would be a hassle. Are there other commands?