MacBook Air storage inconsistent, and all files optimized despite that setting being unchecked

Two-fold storage issues with a MacBook Air, M1/2020, Sequoia 15.6, local storage of 1 TB and iCloud storage of 2 TB.

1. None of the values of storage used are consistent from one week to the next, day to the next, or hour to the next, including when I don't even touch the computer. Also, the GBs used are increasing as I delete stuff.

a) The first time I ran Disk Inventory X a week ago, it said that I had used up 993.3 GB of 994.7 GB on my Macintosh HD. After deleting a lot of stuff, that figure dropped to 826.6 GB. Right now, it's back up to 979.4.

b) Also, that time I read 993.3 GB, Disk Inventory X told me that my photos library was taking up 404.3 GB of storage. Right now, despite having deleted thousands of weighted photos (photos taken with an actual photography camera can use up way more space than those taken by an iPhone camera), it's telling me that my photos library is taking up 572.2 GB of storage, up from 542.5 GB on Sunday and 586 GB on Tuesday. Despite clearing the "Recently Deleted" and not taking any more photos. But when I check my phone, my photos library is taking up 451.73 GB. On neither device are the photo libraries optimized.

c) Another thing is that, according to System Settings > General > Storage, I have over 18 GB used by Messages and over 69 GB (it jumped to 71.24 as I typed that!) used by Applications. On my phone, Messages uses 600 MB. And per Disk Utility, Applications are just 14.4 GB. What's with the difference?

d) On Tuesday, with System Settings > General > Storage, I had 50 GB used by MacOS and 243.97 GB used by System Data. On Wednesday, I had 30.66 GB used by MacOS and (the value System Data did not load). Hours later, I had 39.25 GB used by MacOS and 275.12 GB used by System Data. Right now, those figures are 27.88 GB and 270.81 GB, respectively.

2. Despite having unchecked “Optimize Mac Storage” in System Settings > Apple Account > iCloud > Drive, just about every single file/photo/video on my desktop, in my downloads and documents, etc. is not stored locally. When I hit the space bar to do a Quick Look or try to open it with a double-click, each one takes 30 seconds to a minute to load, if it loads at all. And yet, my desktop is taking up over 100 GB of storage. Essentially, everything is optimized despite me trying to prevent that, is tediously or not at all accessible, and yet still taking up a ridiculous amount of space.

I'm not sure why either of these issues are happening.

If it's relevant, aside from all the photos I got rid of, I also deleted just about every folder in Library with “temp” in the name (many GBs worth of videos which I'd texted to others, redundant files from years ago, etc.) and this weird backup of my desktop. That second one sounds ominous, but the circumstances around its existence are baffling.

(I found it through Disk Inventory X by doing Users > [Name] > Library > Mobile Documents (97.1 GB) > Day One Classic (96.1 GB). Now, for context, I got the Day One app quite a while after Day One Classic was phased out. And the folders and files within the “Day One Classic” subfolder were also created long before downloading the app. When I dug deeper, I found what looked like a backup of my desktop, containing some 80 thousand items and taking up a little over 100 GB, created in March 2024, and last modified this summer.)

All these deletions initially cleared up nearly 200 GB of space, which has since been replaced by the other/remaining categories just growing bigger.

The first issue (of minimal storage available, and never consistently, despite actively deleting stuff) is frustrating enough, but the second one (I can't open anything?!) is actually making my life difficult. Thoughts?

(An EtreCheck report lists my major issues as: Time Machine backup out-of-date, Battery failure, Kernel panics, Heavy CPU usage, and Low disk space; and my minor issues as: High battery cycle count, Apps with heavy CPU usage, Clean up, Unsigned files, and Runaway user process.)