I have the same problem with a .mov file. Here some more informations:
1. Type of the project: Jira Software
2. Next-Gen project
3. Another user and I could add other video files with the same format .mov
4. Yes, its happening to all users
5. There is no way to add this file. Its 11,9MB and I changed to attachment size from 1GB to 2GB.
6. For the console check, please take a look on the 2nd screenshot.
Thank you for reaching out to Atlassian Community!
Testing on my local site, I was able to replicate the same issue, but it was fixed by changing the attachment size. I tested with a 57Mb .mov file and it worked.
I found some errors on the logs from your site related to the attachments:
"level":"ERROR","message":"Could not upload attachment to Media Services"
Searching for similar cases, I found one where the issue was related to the company’s network.
If you are using a VPN, could you please try attaching this file out of the VPN?
If the same issue happens, if possible, test using another network.
Please, take your time to test and let us know how it goes.