Possible HL3/HLX demo - App ID 1275750 (5069770)
Last 2 months I have been very actively tracking through the SteamDB.
One of discussed App IDs rumored to be HLX was 1275750 - According to changes affecting a lot of apps it seems that the project might use Source 2.
Its first occurence at SteamDB was 23 March 2020 (16:14 UTC)
There is a Valve anniversary (30 years) coming up and 2 weeks ago that app got very interesting update -- Yes, updates are coming several per day, but this was different.
Under the App Depot 1275751 was 2 weeks ago added new package 1757151 with the App ID 5069770 - This package is different as its Billing type is set as Free on Demand (This could mean its some sort of demo, press copy or showcase).
From the time (2 weeks ago) that new App ID was added to Depot, both the Apps were updated simultaneously (updates affecting only these 2 projects). But yesterday the Free on Demand app stopped to be updated (seems that the state of this project is now locked in and ready for showcase/demo/press). And further is being updated only the original 1275750 App ID!