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I've been told to start a new thread about this, as the thread I initially posted in is 2.5 years old, although its most recent post before me was only a couple weeks ago, and the issue sounds like the same issue everyone in that thread had.
I had never used LR/LrC before, but decided to give it a try on a brand new MacBook Pro, because my previous photo sorting/cataloging program I only had in 32-bit, which isn't supported by Catalina. But within half an hour of using LrC for the first time, a warning popped up on my screen saying the system was out of resources, and showed that LrC was using 110GB (!!!) of RAM.
I was only doing a relatively minor sync, a few hundred photos on the machine's SSD, and playing with the Slideshow function when it happened. Again, this is a brand new machine, with fresh installs of my CC apps.
The experience makes me never want to touch LrC again. What, if anything, is the remedy for this problem that has plagued LrC for over two years?
Make sure that face detection is paused; make sure that address lookup is paused, and make sure that synchronizing with Lightroom Mobile is paused. Do NOT say "I never turned those on", that's not what I am asking. I want you to look at the settings and confirm these are paused.
Also please state what tasks in Lightroom Classic you were performing when this happened. Was it just slideshow, or were you doing other things just before it happened? How many images in the slideshow?
As I am new to Lightroom, I'm not sure if things are "paused," but the Face Detection box in Catolog settings is not checked and never has been, and the "Look up city, state...." box in Address lookup is not checked and never has been. I just unchecked "Export address suggestions whenever address fields are empty". I have nothing set in the Lightroom Sync settings and no storage taken up online. Is there something else I need to do to make sure syncing with mobile is paused?
And frankly, even if any of those things were on, it is still absolutely unacceptable for LrC to have any reason to use 110 GB of "RAM".
There were something like 7 images in the slideshow. Prior to that I had only started to sync about 1000 photos that take up 6.26 GB on my computer, and had done an export of 112 images, resizing them to 1000px wide. That task had long been completed when I started playing with Slideshow.
I think you would be better off not using Lightroom Classic.
With all due respect, that's a very weird and unhelpful answer.
Roll back to LrC V 10.0 and see if that is better. You do that in the Creative Cloud app. Click on the three dots to the right of the open button for Lightroom Classic.