Export from LR Classic CC to disk ok, but same-time adding to catalogue is way to slow

[innfoto]

Since last update or one before (the one that should increase LR speed especially in export) the export is fast enough (cannot say if it is faster than before), but the pictures that are added to the catalogue at the same time take much, much more time than before. A 50 pictures export to 950px images size at the long side lasts about 20-25 sec. And it lasts 3 minutes to see them (previews) all in LR.

I changed nothing of the hardware, I always run several programs (email...); no software-updates except automatic OS-X updates.

The graphic processing unit was disabled for a test, but didn't show any difference.

What can I test or do more?

Screenshot of System overview:

Thank's for your ideas!

[Just Shoot Me]

See if this helps.

Issues after updating to Lightroom Classic CC 7.2

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Thank You for the link! Sync is not activated. I compared settings to my macbook and found no difference. And the macbook is faster adding pictures to the catalogue, but the macbook should be slower when I look at the CPU and RAM sizes and speed. Now I tried a empty, new catalogue. There things speed up. Also I deleted the previews file some days ago (was > 90 GB), that alone did not help. I guess I have to accept that more than 700.000 images would slow down everything. Still I am sure, that before, when export was finished to disk, at the same time all pictures were added to the catalogue at the same time. Maybe the large previews had to be built up in the background, but I was able to select all freshly added pictures to make for example next exports or a web-gallery.

Any more idea what to check? THX