My only tip is that our “friends” at DxO should have supported Mojave which was the last OS for the Mac Pro. Instead, DxO is captured by its young programmers who as naive youngsters only deign to work with the latest technology.
Consequence – I no longer recommend DxO software to others or advocate for PhotoLab as much as I like what PhotoLab can do for high ISO photos. I’m stuck using an M1 Max now that I never wanted – my own decision to choose PhotoLab years ago cost me €4000 this year not including software costs. While I had PhotoLab 5 working under 5,1 on Big Sur, the pain point on maintaining a stable of Mac Pros on an unsupported OS was enough to push me to go back to a single computer. I could have kept them all on Mojave for another year or two (when I would have been ready to upgrade) were it not for PhotoLab.
That the long answer – the short answer is no, I can’t troubleshoot Mac 5,1 issues now as I’m not using it any more. I didn’t have any issues at the time apart from how time consuming it is to run a computer on an OS for which there is no official support. The MacRumors.com forum does have lots of hands on deck who may help you troubleshoot your situation, if you’ve taken the time to read and research before asking for help.
If I had to do it all over again, I would have moved to Linux fifteen years ago and would be using RAWtherapee instead. At this point in my life, spending years acquiring expertise in new OS and giving up all the software I know would be a poor choice. Back then, I was running a rapidly growing company and didn’t have any free time, hence I very reluctantly didn’t switch. But I didn’t know all the ill and disrespect for its users Apple had in store for us. Steve Jobs was still running the ship and there was no inkling that he’d be leaving both Apple and the world soon. Hindsight is alway 20-20.
The young should flee commercial OS while you can, if you value your privacy and wish to retain any control over your digital environment.