LR Classic can't detect my Nikon D850 for tether

Did you set the permissions for Classic correct in the privacy panel? This is the more common cause of tethering not working. It's described in John's last link: https://blogs.adobe.com/sunil/2020/01/09/macos-catalina-issue-with-nikon-tethering-on-lightroom-classic/ Just making sure. Otherwise, try a different USB cable (yes it annoyingly matters greatly) and make sure to not use a USB hub in between.

This person (on Windows) first started Nikon Transfer 2, which found the camera, and then LR tether started working:

https://community.adobe.com/t5/lightroom-classic/z6-tether-not-working-no-fix-planned/m-p/11073031#M184250

I don't know whether that might help on Mac.

Changing LR's permissions helped with importing from a Nikon via a USB cable, maybe it will help tethering (just a guess):

https://feedback.photoshop.com/photoshop_family/topics/my-d850-wont-tether-to-lightroom-since-9-1-upgrade-works-fine-on-8-4-1-on-another-computer?topic-reply-list[settings][filter_by]=all&topic-reply-list[settings][reply_id]=20386720#reply_20386720

https://blogs.adobe.com/sunil/2020/01/09/macos-catalina-issue-with-nikon-tethering-on-lightroom-classic/

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Click the Apple icon in the upper-right corner, then About This Mac. Which version of Mac OS 10.15 are you running? 

By "suggested Adobe steps", do you mean all the steps in this help document:

https://helpx.adobe.com/lightroom-classic/kb/troubleshoot-tethered-capture-lightroom.html

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