Overlay doesn't work in games using vulkan API

**Game information**
All games that uses vulkan API, such as Portal 2 with -vulkan parameter and Proton/Wine+DXVK.

**Distribution name and version where applicable**
Debian 10.10(Buster)

**Flatpak info**
```
ID: com.valvesoftware.Steam
Ref: app/com.valvesoftware.Steam/x86_64/stable
Arch: x86_64
Branch: stable
Version: 1.0.0.70
License: LicenseRef-proprietary
Origin: flathub
Collection: org.flathub.Stable
Installation: user
Installed: 41.1 MB
Runtime: org.freedesktop.Platform/x86_64/20.08
Sdk: org.freedesktop.Sdk/x86_64/20.08

Commit: b5bc849bc8e5b8ac924a2538a71b342b929d7ca3f1d53e2f2de57e6dea9753ea
Parent: 59ca423d1b9ecd3d6b819c63b070c7ce1c31362b0107cd7287b0005a97d51c4e
Subject: Drop network manager permission This seems to be really wide and if system policies are not set properly, it might allow access to eg WiFi passwords (af6f1609)
Date: 2021-06-20 10:22:15 +0000
```

- Flatpak 1.10.2
- nvidia-460-73-01
- default
- host

**Problem description**
FPS counter and bottom-right notification doesn't appear at all and shift-tab doesn't open steam overlay. Achievements aren't tested.
[term.log](https://github.com/flathub/com.valvesoftware.Steam/files/6872342/term.log)

**Does this issue reproduce with native Steam**
No