E2E image and file uploads not working in desktop app, in web browser is fine

[hrabotoner]

Description:

In E2E channels, uploading images results in a Retry placeholder:

And uploaded files can't be downloaded (nothing happens when you click on download icon or file name).

This only happens in flatpak desktop app and Electron .deb app: https://github.com/RocketChat/Rocket.Chat.Electron/releases , in web browser both work fine.

The workaround that used to work in version 6.12.1:
Settings -> End-to-end encryption -> Encrypt files = OFF
doesn't work anymore after upgrading to 7.4.1 - instead I get a Not allowed message from rocket.cat bot:

Steps to reproduce:

Upload an image or file in E2E conversation.

Expected behavior:

E2E uploads work

Actual behavior:

E2E uploads don't work

Server Setup Information:

• Version of Rocket.Chat Server: 7.4.1
• License Type: free
• Number of Users: 50-100
• Operating System: Linux
• Deployment Method: docker
• Number of Running Instances: 1
• DB Replicaset Oplog:
• NodeJS Version: v22.13.1
• MongoDB Version: 6.0.14

Client Setup Information

• Desktop App or Browser Version: 4.3.0
• Operating System: Linux

Additional context

Relevant logs:

[hrabotoner]

Could this be due to faulty nginx configuration? Does anyone else have this issue?