LR Classic takes forever to load and it is impossible to change from one photo folder to another one.

I have been a long time LR user and the program has been working flawlessly until I had to move to LR Classic because I didn't want to move my photos to the cloud.

Recently, LR Classic has become a nightmare and it is nearly impossible to use it.

When opening it, it takes 5.5 minutes to open the catalog and show the quantity of files in each folder.  Then, it is possible to move to a folder and do some work.  However, when I try to change folders, it freezes and the only possible action is to close it.  When reopening it, I have to wait again for 5.5 minutes....  A nightmare !

When working inside a photo folder, the performance is OK at first but degrades gradually.  After a while, it becomes so slow I have to close LR and start again.

I have 60,000 photos in 1 catalog (724,496 Kb) and the standard-sized previews folder is 64,104,779 Kb).  Both are on the SSD C: drive, which has 17% free space.  LR is also on this drive.

The photos are on the 😧 drive and take 925 Gb.  The drive has 32% free space.

LR, Photoshop, Camera Raw and Creative Cloud are all the latest version. The O/S is W10 64 bit and all updates are current.  I use the Graphics Processor, a NVIDIA GeForce GTX 750Ti.  The Intel i7 processor speed is 3.6 Ghz and the computer has 16 Gb memory.  The LR Camera Cache Settings are set to 20 Gb on the 😧 drive.

Can anybody help me on this ?