Hi
@SPJones! I also have an iMac late 2013 (i7 CPU 24GB RAM and nVidia GTX780M 4GB VRAM).
ONE
From what you say I deduce that you too, like I did, have dissociated the two disks of the Fusion Drive to replace the mechanical HD with an SSD.
If so,
surely you can install Catalina on the internal 128GB Apple SSD! In fact, in my opinion...
you have to install it because this way you will always be sure that your Mac will always be bootable even if Apple (as perhaps they are about to do) blocks Ventura in unsupported Macs via hidden security updates which is a new future feature of Ventua.
So Catalina will be useful at least while waiting for a new OCLP build to fix the problem.
TWO
Why do you say you're not with Ventura? Everything works fine for me and if you look for my previous post you will see that I explain how you can also activate the "Live Text" and the automatic removal of image backgrounds... In fact these functions are blocked by OCLP because in some Macs they cause blocks and KP, but our iMacs (at least mine) are immune to these problems.
For me, therefore, everything works in Ventura and not only Acrobat Reader, but also Acrobat Pro, Photoshop (latest 2023 version), etc.
All macOS system and all apps work 110% better than Catalina. Also Stage Manager works stupendly... Geekbench 6 tests are also outstanding and give equal or superior results to several 2019 and 2020 Macs…
A sign that Apple didn't make the most of the iMac hardware until Catalina or maybe they held hardware voluntary back...
The fact is that since - in theory - Ventura shouldn't work with my iMac, perhaps there are no more blocks in the macOS code and the Mac, therefore, fly...
[Note: the only application that doesn't work in Ventura is "Continuity Camera" and its equivalent app, Camo, also doesn't work, but it works great in Catalina].
Bye