Persistent as I am, despite the negative comments, here is a method and a script to save your logfiles to TMPFS. Many thanks to @DL6ER for the instructions.
Of course, again, if the TMPFS is full (no more RAM disk space), pihole-FTL will probably fail, so choose your TMPFS size carefully.
Whenever a new version of any software I use (raspbian, webmin, unbound, knot-resolver, munin, wireguard, pihole, …) on my pi, I reinstall everything on another SD card, scripted, takes about an hour. Worth the effort to have the latest versions running...