MBP5,2 17" 2.8GHz mid 2009, 8GB, APFS ROM patch applied, Samsung SSD 860/840 EVO with APFS.
Using 10.14.6 Supplemental on the internal SSD as my standard system. Patcher 1.3.3 used to download it and to produce a USB installer. Very stable like 10.14.5 was.
Also using experimentally 10.15.0 DP5 on an external (USB) SSD. Patcher 1.0.6 used to download it. Chose option "Disable APFS Booter" then did "Install to This Machine" which already had an earlier Catalina on it, without problems... And happily using Photos! It seems Catalina provides all I need and the MBP5,2 can serve me well in its 11th year.
Thanks to
@dosdude1 and everyone for the Catalina, Mojave (and predecessors) support!
One thing I had observed after installing DP4: I got frequent sleep/wake failures after a while in Catalina as well as after booting back to Mojave (one of several equal reports attached). That stopped after resetting SMC and NVRAM. Had first suspected a hardware problem related to very hot weather conditions... anyway all fine now, including in Catalina. Will diagnose more carefully should it happen again.
@Larsvonhier and
@albertdrake had reported sleep/wake failures in Mojave a while ago under different circumstances.
BTW I keep user data on the Catalina disk up-to-date with CCC to the Data part of the disk, while running Mojave. I do that for most user data except Photos library to avoid lengthy re-formatting, except Mail, and except Applications.