New filesystem on a removeable disk can't be written by a common user

# mkfs.ext4 /dev/sdc1
# mount /dev/sdc1 /mnt
$ touch /mnt/a
touch: cannot touch '/mnt/a': Permission denied

(root can write)

With automount in Dolphin, a common user also has no write permission.

How to make it writable by a common user?

Please search the forum - the question has been asked countless times.

Hint: chmod ugo+rw mountpoint