(Reported experimental version: experimental-6.3-20210719)

I had to downgrade the app to the previous version using DepotDownloader

First install the dotnet tool for your system, e.g. for Ubuntu:

sudo snap install dotnet-sdk --classic --channel=5.0

Then download DepotDownloader from the link above and extract the archive.

Open a terminal in the extracted folder to download the previous version using the following command:

dotnet DepotDownloader.dll -app 606180 -depot 606181 -manifest 335476331331916300 -username <SteamID>

It will prompt you for your Steam password and confirm the login with 2FA.

This will download the previous version in subfolder depots/606181/6328004. Now backup your Viveport Video installation folder, and copy the downloaded files there. That’s it, you can run that version though Steam.

You probably want to keep the downloaded files in case Steam decides to update Viveport Video.

I noticed some lag on a 360 VR video