Marathon
Final Fantasy 14
Football Manager(any)
Diablo IV
Civilisation (7 I guess...)

I don't think I could just pick my 5 favorite games, because not all of them have a ton of content. (For example Katamari Damacy is a great game, but it's pretty short.)  My 5 picks would be:

1. Heroes of Might and Magic 2
2. Freedom Force
3. Final Fantasy Tactics
4. Dark Souls
5. Final Fantasy 11

(Got include that last one just because it has a mountain of content.)

Can i play them online assuming other players will be available or is this a desert ksland sitiation?

Minecraft + mods
Sekiro
Starcraft
Two point hospital
GTA provided the server are running and nodded

This might feel a bit cheaty because of mods on the first 3, but let's-a-go!

1. Hearts of Iron IV: With mods, there's endless time and scenarios. I'm currently playing 2 alternative realities where either Imperial Germany won WW1 (Kaiserreich) or the Axis won WW2 (TNO), a modern day version (Millenium Dawn) and a... My Little Pony: Friendship is Magic! mod (Equestria at War)
2. Oxygen Not Included: Again with some small mods, but this is a game I always come back to even when I don't want to for some reason.
3. Baldur's Gate Enhanced Edition Trilogy: A mod that combines Baldur's Gate I, II, their expansions and their spin-offs into one giant game.
4. Wizardry 8: Best RPG ever, and also pretty long, perfect to kill some time if you only have 4 other alternatives...
5. Growing up: for some lighter stimulation, here you guide a child from conception all the way to Adulthood in the 80's and 90's. Perfect if you have little time, as the others are all huge time-killers.

Octopath Traveler 2
Pokemon Firered/Leafgreen
Mario Galaxy
Xenoblade 3
DBZ Budokai 3

You can play them online, definitely

1. Rocket League
2. DJ Hero 2
3. Tetris
4. Borderlands 2
5. TBD

Privateer 2 (spinoff of my favorite Wing Commander series, space freelancer game)
Crush! Deluxe (scifi sports strategy)
Okami (PS2)
some racing game where you can make infinite amount of tracks (or download hundreds)
some Battlefield/Battlefront, maybe just the original SW: Battlefront (assuming there's infinite supply of players and mods/maps)