LRC Mac Backups have inflated in size by a lot

"Also all my lrcat files are tied to v13-3.  I have lrcat files for v10, v10-v11, v12 and v13."

Prior to LR 14, the default name for each upgraded catalog included the Lightroom version number. But starting in LR 14, it no longer does.  So your LR 14 catalog contains "v13", and your LR 15 catalog will also contain "v13". See the section Catalog Upgrade (Classic) in these release notes for more details:

https://www.lightroomqueen.com/whats-new-in-lightroom-2024-10/ 

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To see precisely how many photos have been denoised:

1. In Library, select All Photographs.

2. Do the menu command Photo > Stacking > Expand All Stacks.

3. Configure the Library Filter bar's Metadata browser to have a single column, Has Denoise:

"Yes the box to automatically write changes into XMP is checked.

"As far as Denoise, ... but I only use it on high ISO files.  Most of my photos are outdoor landscapes so ISO rarely goes above 400.  Only when I photograph interiors of old cathedrals do the ISO go over 1000 and I've used AI Denoise on those shots but they're like 5% of my library in the past year or two.

"All those lrcat files are just a gigabyte or two and they're 1-2 years old."

I think you've tripped over a severe performance bug introduced in LR 14.4 and not yet fixed:

https://community.adobe.com/t5/lightroom-classic-bugs/p-automatically-write-changes-to-xmp-can-t-be-used-with-denoise-on-large-numbers-of-photos/idi-p/15393188

When you have Automatically Write Changes Into XMP enabled and you denoise larger numbers of photos, your .lrcat file will explode in size.  This bug will typically cause 10 MB to 20 MB on average (sometimes much more) to be added to the catalog for each photo you denoise.   So if you denoise just 1000 photos, that could add 10 to 20 GB to your .lrcat file!

The only way to avoid further growth is by disabling the option Automatically Write Changes Into XMP and to never manually invoke Metadata > Save Metadata To File.

While Adobe has acknowledged this bug, we have no idea if they're going to fix it -- they rarely indicate ahead of time which bugs they're going to fix when. And even if they do fix it, they may not purge the unnecessary data the bug previously added to your .lrcat file.

In general, writing metadata back to files and metadata status has gotten more and more flakey over the past few years, and it sure seems that Adobe may be abandoning it for all practical purposes.

Also all my lrcat files are tied to v13-3.  I have lrcat files for v10, v10-v11, v12 and v13.  All those lrcat files are just a gigabyte or two and they're 1-2 years old.

Adobe keeps changing the Catalog format and with new versions, they upgrade to the latest catalog format for whatever LRC version they release.

Yes the box to automatically write changes into XMP is checked.

As far as Denoise, I don't recall how long the AI Denoise feature has been available but I only use it on high ISO files.  Most of my photos are outdoor landscapes so ISO rarely goes above 400.  Only when I photograph interiors of old cathedrals do the ISO go over 1000 and I've used AI Denoise on those shots but they're like 5% of my library in the past year or two.

Looking more at my Catalog Settings, my Preview Cache is 28 GB, standard Preview Size is 1440 pixels and Preview Quality is Medium.

But Preview Storage Managemet is set to Automatically Discard 1:1 Previews After 30 days.

Hmm, in addition to the 16 GB .lrcat and lrcat-data files, I have a 30.5 GB Previews.lrdata file.

Why are there so many different lrcat files?

Back in January, it apparently wasn't generating all these huge multi GB files.  It seems that LRC has changed the way it saves these lrcat files, not that additions I made to my Library caused all these lrcat files to be created.

So your catalog takes about 16,000 MB / 84,727 photos = 188 KB / photo.  My catalog of 41,000 photos takes 65 KB / photo, 3 times less.

1. Have you set the option Catalog Settings > Metadata > Automatically Write Changes Into XMP?

2. Have you applied Denoise to hundreds or thousands of photos?

Current .lrcat file is 16 GB and there is also an .lrcat-data which is also 16 GB.

There are a total of 84727 photos in the catalog.

I've added photos to the library between January and now but we're talking maye 10,000 photos tops.

Since my January 19, 2025 backup folder is right around 500 MB, something changed.  Sure more photos in the catalog than back there but looks like the catalog file just grew some ridiculous amount.

I haven't unzipped the old Backups but I wouldn't thinkthat the unzipped catalog would be 10 GB or greater if the zip file is under 500 MB?

Maybe your catalog has gotten much larger in size, perhaps tripping over at least one known bug.  To rule that out:

1. Do Catalog Settings > General > Show to open Finder on the current catalog folder.

2. What's the byte size shown by Finder for the <catalog>.lrcat file in that folder?

3. How many photos are in the catalog (in Library, look at All Photographs in the upper-left corner)?