Can't open more than one file at a time in Illustrator 25.4.1

[birckcmi]

I'm using Illustrator CC 25.4.1, on an old Mac Pro running Mojave 10.14.6. My GPU is an Nvidia GTX 650, with 2 GB VRAM, and I have 48GB RAM. Lately, after years of success, I've been unable to open more than one Illustrator file at a time. That definitely queers the do. And, presumably because of the age of the computer (late 2012), I can't update the OS, and thus can't update the version of Illustrator. At least that' my presumption. When I try to update Illustrator or any other Adobe CC product, the update is listed as "Not compatible". So need to find a way around this problem. If I have to stay with AI version 25.4.1 or even drop back to an earlier version, fine. I just need something that works properly. Any Suggestions?

(note-I wrote a less-informative version of this post elsewhere in the forum) 

[Anshul_Saini]

Hi there,

Sorry to hear about your experience. I would request you to share a few more details like:

• Does it hang, or does nothing happen when you try to open more than one file?
• Is this happening with all the documents, old & new?
• Where are your files saved (Network Drive/ System HDD/ Shared Folder on System/ External HDD)?
• When did this start happening? Are there any recent changes made to your system? For example, any antivirus, system updates, plugins, or web extensions installed recently.
• Does resetting Illustrator Preferences (https://helpx.adobe.com/illustrator/using/setting-preferences.html) help to resolve the issue?
  Disclaimer: Please note that resetting preferences will remove all the custom settings, and Illustrator will launch with default settings. You can also take a backup of the folders in case you want to. Location is mentioned in the article.

We are here to help. We just need more information.

Thanks & Regards,

Anshul Saini

[Met1]

What size are the Illy docs you're trying to open? Do they have lots of placed files? Vector or pixel?

[birckcmi]

Here's the solution, Courtesy of Monika Gause:

https://helpx.adobe.com/contact.html

I still dn't know why the one-file-at-a-time-only phenomenon showed up, but because nothing I knew to try could fix it, I decided that my only recourse was to re-install a clean version of Illustrator. Ordinarily, that can't be done, but the above link took me to a CC page that saved the day. For those on computers that are too old to update out of Mojave to Big Sur, it is possible to re-install a fresh version of the application immediately preceding the update-in other words, my version of Illustrator, version 25.4.1, the last version that can run on Mojave.  I followed the instructions, installed AI anew, and it works fine. No problem opening multiple files at a time.  I still don't know why the problem appeared when it did, but it no longer matters.

[birckcmi]

Correction : Installing a clean version of Illustrator CAN be done ordinarily, but in my case, the newly-updated version was the only one available-I thought-and it was "non-compatible" with my system.