Glad to hear your update.
I would definitely explore a new lab before diving in to a new calibrator. I've no reason to think there's anything wrong with your Spyder5.
The same way that I showed you on another photo, I think. Duplicate a chunk of the Background layer, set it to "Multiply" mode, nudge it down a bit, then mask it on gently.
It sounds like it's doing everything right. Are you following my instructions here? https://www.damiensymonds.net/cal_S5P_mac.html
The "Target" of 120 is not important.
What's important is the "Current" number. What does yours say?