Bad UX when screensharing in fullscreen

### Steps to reproduce

1. be in a fullscreen call
2. click on screensharing

### Outcome

#### What did you expect?
- the screen sharing modal comes up
- clicking multiple times only creates one screen sharing modal

#### What happened instead?
- the screen sharing modal is hidden in the background behind the fullscreen call, prompting to click again
- there is one modal per click (in the background)
- i realize this is the electron sharing dialogue at work here, but this is unacceptable UX for your app

#### see also
vector-im/element-web#19181

### Operating system

arch, w10

### Application version

1.10.11 and newer nightlies

### How did you install the app?

element.io, arch repos, aur

### Homeserver

1.57.1

### Will you send logs?

No