Extremely poor screen sharing performance and severe lag

### Steps to reproduce

1 Join a video call on the Element desktop app.

2 Start screen sharing.

3 Attempt to navigate or present content while sharing.

### Outcome

The screen share quality is terrible, with severe lag and low frame rate, making it virtually unusable.

### Operating system

Windows

### Application version

1.12.26

### How did you install the app?

https://element.io/en/download?cta=hp

### Homeserver

@kelyan24:matrix.org

### Will you send logs?

No

Reproduce the issue in the Element desktop app on Windows using version 1.12.26: join a video call, start screen sharing, and navigate or present content. Compare the screen-share frame rate and lag with expected behavior, then use the available issue details and request logs if further diagnosis requires them. Done means screen sharing is usable without severe lag or low frame rate.

Written by the indexing model from the issue text.