I have Pi-hole v5.16.2 FTL v5.22 installed on Ubuntu Server 22.04.2 LTS. I've had this instance installed for quite a few months now, and I've never seen this error before:
Since discovering this issue I've not changed anything, so I'm open to advice. I did think about it being possibly solvable by altering the retention period, however according to this post that shouldn't be an issue.
This is not an error, it is a warning.
Our default warning occurs at 90% of disk space used. You can change this so you are no longer shown the warning.
https://docs.pi-hole.net/ftldns/configfile/#check_disk
Note that the warning is not telling you that the query database or the FTL log is using 92% of your disk space; it is telling you that the total disk space available is less than 10% of the total.
To complement jfb's informaton:
Your debug log shows your Pi-hole's databases to contribute less than 1G of storage:
*** [ DIAGNOSING ]: Pi-hole FTL Query Database
-rw-rw-r-- 1 pihole pihole 856M Mar 28 19:02 /etc/pihole/pihole-FTL.db
*** [ DIAGNOSING ]: Gravity Database
-rw-rw-r-- 1 pihole pihole 42M Mar 27 21:14 /etc/pihole/gravity.db
You may want to find out what is filling your storage before you actually hit the wall, e.g. by running
ncdu /
(provided that ncdu is available and installed on yor system).
Note that it may take a long while for scanning your drive.
Thank you for both of the responses, I've ran ncdu and found the culprit. I was just confused at first as it mentioned specifically the log and db file but thank you for the explanation 
The message mentioned those files because the disk space was calculated while Pi-hole was updating the log and the database with new information.
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