Extremely slow startup for Lightroom

After updating to LR 7.3, I began having issues with very slow startup, which has persisted through purchasing a new iMac (2017, with a 1 TB fusion drive and 16 GB of RAM, latest OS). The slow startup has persisted through both of the recent updates, and is still happening after reverting to 7.2, which solved the problem before my new computer. It has taken up to 5 minutes to fully load Lightroom, and it is very frustrating as I watch the memory usage slowly go upward on the System Monitor, all the time saying Lightroom (Not Responding). I have been using Macs since the Classic, and have never been so frustrated in my life.

When I start the in Safe Mode, Lightroom loads in 15 seconds or so. It is also much faster to load if I quit LR and start in again, taking perhaps 30 seconds instead of 5 minutes.

GPU acceleration is not enabled.

Am I having hardware issues (cache problems with the Fusion Drive), OS issues, something else? I even pulled the 8GB of RAM I  purchased the computer, and replaced it and pulled the RAM that came with it, and no change.

I reset the Systems Manager, per advice from Apple support, and it loaded quite quickly, but the next day, when I restarted my computer, the same old slow load happened.

There seems to be no telephone support option for the LR/PS monthly bundle, which is also very frustrating. Why?

Help would be very much appreciated!!!

Thanks