First question here, but long time pi-hole user. I installed pi-hole so long ago it is on raspbian stretch.
Details about my system:
pi 3B on raspbian stretch, serves home lan .
What I have changed since installing Pi-hole:
Only updated pi-hole and done apt-get update/upgrade cycles.
Short question, can I do dist-upgrade, or should I start fresh with the latest raspbian? I found a thread on here saying dist-upgrade was deprecated, but that was from 2017 and I wonder if the advice is still the same.
Also if I start afresh, how do I transfer over my dhcp fixed IP allocations and other settings?
You can do an in-place change of distribution by editing your sources lists, but this is not recommended by Raspberry Pi OS maintainers. I have done this on about four Pi's, with some good results but not all good results. It's a crap shoot.
I recommend a fresh install of Bullseye, then a fresh install of Pi-hole on that. To transfer your existing Pi-hole settings to the new install, export them using the teleporter function (web admin GUI > settings > teleporter), and then you can import them into the new install.