It appears that FTL does not respect the TTL in the DNS record.
This is a bug and should be fixed.
In the meantime, the documentation says that you can turn off caching by setting cache-size to zero.
If I do this, FTL refuses to start.
Pi-hole Version v4.3.2 Web Interface Version v4.3.2 FTL Version v4.3.1
The config file has a comment insisting that you don't modify it, but override values in your own config file. However, trying to override config-size gives this result:
Nov 12 22:52:09 raspberrypi systemd[1]: Started User Manager for UID 999.
Nov 12 22:52:09 raspberrypi pihole-FTL[1171]: dnsmasq: illegal repeated keyword at line 33 of /etc/dnsmasq.d/01-pihole.conf
Nov 12 22:52:09 raspberrypi dnsmasq[1212]: illegal repeated keyword at line 33 of /etc/dnsmasq.d/01-pihole.conf
Nov 12 22:52:09 raspberrypi dnsmasq[1212]: FAILED to start up