Most likely related to partitioning, check if it is an ntfs partition and if so change it to ext4.

Originally posted by Visualvengeance:

Most likely related to partitioning, check if it is an ntfs partition and if so change it to ext4.

How do I do that?

Probably ntfs partition. If you want to use ntfs you should use the ntfs-3g fuse driver, not the ntfs3 kernel driver. The ntfs3 driver causes read errors on a regular basis, likes to set the dirty flag, sometimes refuses to mount the drive or sets permissions to root:root r-xr-xr-x so you won't be able to write anything unless root.

@Sixteen60

Can you run the following command from the terminal?
lsblk -o NAME,LABEL,TYPE,FSTYPE,MOUNTPOINT

Example:
[AngryBeard@archlinux ~]$ lsblk -o NAME,LABEL,TYPE,FSTYPE,MOUNTPOINT
NAME LABEL TYPE FSTYPE MOUNTPOINT
sda disk
└─sda1 part ext4 /mnt/steam
sdb disk
└─sdb1 TIAMAT part btrfs
zram0 zram0 disk swap [SWAP]
nvme1n1 disk
└─nvme1n1p1 HOME part btrfs
nvme0n1 disk
├─nvme0n1p1 ROOT part btrfs /var/tmp
├─nvme0n1p2 BOOT part vfat /boot
└─nvme0n1p3 HOME part btrfs /home

Is you External drive empty or does it already contain data?

Such problems are almost always due to two reasons.
- steam installed as a flatpak sandbox package.
- windows cursed ntfs file system (use only as a last resort)

You now have two paths.

You can cover the hole in your shoe with mud and avoid the puddles - grant access for flatpak, and mess with ntfs
Expect further problems in the future.

You can do it as you should.
Uninstall flatpak and install the official version of Steam using apt.
sudo apt-get install steam
Format the partition to ext4.
gparted
It will probably be easiest for you.

Originally posted by grzegorz77:

Such problems are almost always due to two reasons.
- steam installed as a flatpak sandbox package.
- windows cursed ntfs file system (use only as a last resort)

You now have two paths.

You can cover the hole in your shoe with mud and avoid the puddles - grant access for flatpak, and mess with ntfs
Expect further problems in the future.

You can do it as you should.
Uninstall flatpak and install the official version of Steam using apt.
sudo apt-get install steam
Format the partition to ext4.
gparted
It will probably be easiest for you.

My guess: He has a steam library from a windows machine on that external drive and wants use it on a Linux machine.

Which as we both know, doesn't work.

Edit: You can try to shrink the NTFS partition, Create a new ext 4 partition and keep two steam libraries. Its a little complicated and has a risk of data loss

In the windows 8 and later, because they pretend to be turned off while still running (quick start). I suggest shrink ntfs from the windows level.
Yes, the same library will be a source of problems. Although one can compromise in the case of large games (separate folder).

OP, we need more info about how the external SSD is set up. If you just pulled it out of a Windows machine or installation, then all the points everyone mentioned are correct: you should use an ext4 partition type for Steam on Linux not NTFS. But be careful! If you need all the content on that drive, reformatting will wipe everything on the drive! So move everything on it off somewhere else temporarily while you set it up.

Can confirm this. Downloaded the official steam installer for linux from the site (using Pop!_Os). Since windows was previously installed on my machine all my secondary drives were still using the ntfs file system and games would immediately crash if booted from this drives. After changing to an ext4 partition the games all work now. For my usecase I Also had to make changes to /etc/fstab to mount the drive properly when booting since te uuid changed when creating the new partition and also had to give the right permissions to the mounted drive.