Error when creating partition in Gnome Disks

I'm on Pop!_OS with 4th gen i7. I have a 1TB 2.5' SATA SSD that's been put in an enclosure. I used Gparted to create a 'gpt' partition table. Then I installed btrfs-prog. Then I used Gnome Disks to try to create a BTRFS partition with LUKS encryption.

But I got this error:

Error formatting volume

Error creating file system: Command-line 'mkfs.btrfs -L '1.0 TB Storage Disk' '/dev/dm-1" exited with non-zero exit status 1: stdout: 'btrfs-progs v5.16.2
See  for more information.

NOTE: several default settings have changed in version 5.15, please make sure
this does not affect your deployments:
- DUP for metadata (-m dup)
- enabled no-holes (-O no-holes)
- enabled free-space-tree (-R free-space-tree)

'
stderr: 'ERROR: error during mkfs: Operation not permitted
' (udisks-error-quark, 0)http://btrfs.wiki.kernel.org

Looking at the SSD in Gparted, it had 1 unallocated partition with a yellow exclamation mark at first. After creating the partition table the mark was gone.

And now after using Gnome Disks, in Gparted in 'File System' it's a black box with '[Encrypted] unknown'. The middle partition is sandwiched between two tiny unallocated partitions. Upper is 32 Mib, lower is 9.24 Mib. The SSD did ask for the password I set when I plugged it in, so that worked.

If I now use Gparted to format this unknown partition to BTRFS, it turns from black to orange. Right clicking it, 'mount' is greyed out. But in file explorer, 'mount' is an option with the disk, which shows up now in the sidebar.