fortwodriver
Mu-43 All-Pro
Yeah, I remember LR not doing too great with that many spot heals, too. I assume your working drive is NVMe/PCIe storage? That seemed to be one of the best improvements I noticed, other than having a larger display so less panning and zooming was needed.
I'm on a 2012 Mac Mini. I've worked with 40MP+ files before in LR from other cameras, and yes, once you start spot retouching it can get quite slow as it keeps track of all of that in real-time. For some reason Photoshop, in all its complexity handles retouching FAR better than LRC. I just chalked it up to LRC being a bit of a resource hog.
I switched to C1 earlier this year for other reasons, but I still have my Adobe subscription.