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)

It needs to be something with a lot of replayability, so, assuming there's no online multiplayer, and there's no other people to play board games and tabletop RPGs with, something similar to this:

- Kerbal Space Program, for ability to infinitely mess around with making rockets/spaceships and test them in proper orbital mechanics, while retaining whimsical nature (or Kitten Space Agency, which is spiritual successor involving some of the same people from KSP1)

- some war sim, probably something from either Combat Mission, Steel Panthers or Battlegrounds/Campaigns series...I haven't played anything new from this very niche genre for quite a while, so I would need to check on what's new there as well

- some management sim, either some Civ-like or SimCity-like

- something lighthearted, either MK8 Deluxe, for the sheer size of its content or something simple like arcades from Golden Arcade age of 80s, like Galaga

- either something like Sid Meier's Pirates!, for it's open world privateering where you can finish one "career" in one sitting, something like Elite (whether it's actual Elite, like First Encounters, or some of games influenced by it) for its open ended space exploration, OR Kenshi or Mount&Blade for their open-ended worlds with no predetermined goals OR some Rougelike (like Dwarf Fortress, Caves of Qud or ADOM)...this 5th entry would probably take by far the most time to decide what should I pick

5 games is just not enough, no matter what you pick in the end...