How to get achievements in Half-Life 2 (20th Anniversary Update) if you got them earlier in episodes

1. Install Half-Life 2 (now it already includes all episodes):

https://store.steampowered.com/app/220/HalfLife_2/

2. Launch and close the first episode: 3. Launch and close the second episode: 4. Launch Half-Life 2 and you will immediately receive achievements:
Note: The commands should be executed in Windows Run (Win+R).

Alternatively, you can manually install and launch episodes through Steam interface.

Make sure that your library shows "Tools" (it's in the same place as "Games", "Soundtracks", "Software", "Videos"):

Then, through the search, find, install, launch and close the episodes and then launch Half-Life 2.