I can't get more than 1885 photos to work when running actions in the latest version of Photoshop.

Here. You can just search for %TEMP%.

If you have the scratch disk on a separate drive, it will just be at the root of the drive (not in a folder).

I'd love to observe that too.
If there is any way to know the usage of the scratty file while the batch file is in progress, please let me know

@Kevin Stohlmeyer 

OK, so now I've run the test again, this time keeping a very close eye on the Photoshop scratch file as the batch runs.

I just cannot get the scratch file to grow as the batch progresses, no matter what I do. It only bumps a bit when there is a particularly big file in the batch, so that it has to expand a bit to accommodate that. And then it stays put, unless there's an even bigger file ahead.

This time I used a more complex action, and when that batch had finished, I ran another action on the same batch. The scratch file stayed essentially the same throughout.

This is on Windows 10 pro if that matters. I have the primary scratch disk on the system drive. It's a PCIe 4.0 NVMe, so extremely fast. Don't know if that matters either.

EDIT, afterthought: Maybe disk speed does matter. Overwriting takes a bit of time, and if there's not enough time to delete the previous scratch data, then perhaps it could grow - until the disk catches up. Just a thought.

OK, I'll test again later, gotta run now. I'll monitor the scratch file real-time while the batch is running.

@D Fosse thats not what Im seeing - at the end yes it does release but only after its completed.

During though it increases and does not release between files.

@Kevin Stohlmeyer 

That does not happen here. I just tested it now. The scratch disk space is reused.

I took a folder of 105 images, and first ran a batch on 6 of them to get an "average" scratch file, which was around 15 GB.

Then I ran the batch on the full folder of 105 files. At the end I still had a scratch file around 15 GB.

Granted, this was a simple action that didn't do much more than resave to a different folder. I'll try on a more complex action that will produce a bigger scratch file, later when I have time.

@D Fosse when running batch scripts - closing a file or not - scratch disk will get used and not release giving this a finite cap. When the scratch disk is full the script will stall/fail.

@digicube Go to Photoshop Help Menu/System Info and copy/paste details in a reply. Post only once as the system takes time to process the large amount of data.

Monitor your scratch disk space as the script runs, as you will see PS is not releasing/recycling disk space until the script completes.

To be clear, RAM isn't all that important here. There is no such thing as "enough RAM" anyway. The heavy load is handled by the scratch disk, and that's what you need to monitor. Running out of scratch disk space will kill Photoshop.

But with that said, running a batch that closes one file before processing the next, will not "use up" memory (real or virtual). Memory and scratch disk will be reused and recycled.

So as long as there is scratch disk space, a batch could in theory run forever. Maybe there's a limitation in numbers, I don't know. I have never tried a 1900 file batch, but I do often run several hundred, and have never seen any problems.

Not enough?
The Sony a9's 1865 ARW files are only 43G in size.
The system memory is 383G.
Of course, the ARW files are compressed, so once they are uncompressed and in memory, they will be much larger. (6000*4000*16bit)
However, when I created the action file, I created an action to work on one file and then exit the file and start working on the next file.
I don't think it's possible for all the files to be in memory.