Unlikely to be it since it’s nowhere near from the last 10 years, but CITY 2000 seems like it could be similar at least artistically?

I think the best I can recommend is looking through Steam, searching for “London” and the mystery genre. I didn’t quite catch anything there that fit at a glance, but maybe you will. Similarly could be done on GOG, since it sounds like it could potentially be an older game? Or itch, but maybe the best way to search for that would be by googling london missing friend mystery site:itch.io.

I’m assuming a modern setting, with no supernatural elements and the mystery genre, so that’s the best I could do. It’s going to be very hard to find something without some details being fixed. Point and click? Photos or isometric? Is the player character visible? Do they have any identifying details? Does the pub have a name? Anything like that could do a lot.

You say you watched someone play it on youtube then you might be able to search your youtube viewing history?

Late and I cannot possibly read everything here, but I’ll come back to it as well.

And just to do some due diligence:

• Saw it multiple times already, but Homeworld.
• Star Wars Rogue Squadron or many of the other Star Wars flight games before it.
• Imperium Galactica 2. Amazing space RTS with space and ground combat.
• I think one of the Formula 1 games from the era is considered among the best, but I’m not sure which. If you like F1 and racing that’s worth checking out.
• Star Trek Armada is from 2000, but very good too.
• Sid Meier games.
• Nintendo games, including Mario Kart 64. Unfortunately the first Mario Party isn’t as good as modern ones I hear, but may also be up your alley.
• Scorched Earth or Tank Wars for DOS. Worms for a more modern take on the genre.

Very space- and RTS-themed, but that’s what got my attention at the time. And they were having their golden age. Also I was very young in the 90s, so that’s all I have.