As you can see, you have no swap partition, but instead you have formatted /dev/sda4 as ext4. The swap flag in the partition table does not reflect what’s on the partition ─ it is only a flag.
If the filesystem on /dev/sda4 is not mounted anywhere, then you can reformat it as a swap partition by way of mkswap. Be sure to then also add it to /etc/fstab with the proper UUID.
More information below…
man mkswap
man fstab
The tutorial below also contains a section on /etc/fstab.
