Assuming the partition you are trying to mount is NTFS, try this:
sudo pacman -Syu ntfs-3g
echo 'blacklist ntfs3' | sudo tee /etc/modprobe.d/disable-ntfs3.conf
Close and re-open Thunar, to see it that helps; and report back with the results.
Otherwise;
Please provide the output of:
cat /etc/fstab
… and:
lsblk
… and:
inxi -v7azy
… and, please read the following useful tutorials:
1 Like