the game is single player and indies dont usually use drm.

Seems to be more complicated than that. :/ On the other PC, it also opened the browser to login to Epic Games, but ignoring that or closing the browser means the main menu doesn't appear. Earlier on my laptop Epic identified my account automatically and asked permission to share account data with the game. Pressing Deny there let me play the game in offline mode, but I have no idea what would happen if you tried with an Epic account that doesn't have the game.

Edit: Apparently, Kena requires an Epic Games account. Not logging in means not reaching the main menu. I don't know if there's an ownership check before that permission request thing, but if I were to hazard a guess, I'd say there is. Even if there isn't, you need an account just to deny the permission request, in which case the game tells you it'll run in offline mode and neither the pre-order nor the deluxe content will be available.

Oh, that really sucks. :-\ I was really hopeful for this one, but I guess I'm waiting for the Steam version. I appreciate your willingness to check.

I wonder what browser you are talking about. Your regular standard web browser?

As an option, It was announced that there will be a physical PS4 and PS5 version.

Correct.

Thanks for testing this stuff in detail on a 2nd PC. +1. I'm tempted to change the original guidelines from simply "renaming the Epic Games launcher's .exe" to actually requiring testing on a 2nd PC that never had the Epic Client installed as there seems to be a lot of new complications like this where "pops up a browser window but can be dismissed" doesn't always work the same on a PC where the Epic Launcher was never installed. Although it means fewer people are able to test, it rules out a lot of issues such as perhaps the Epic Games Launcher is storing some account credentials in a file or token somewhere else (eg, under C:\Users\AppData\ or My Documents) and games are looking for that. It also safeguards against Epic introducing potential "silent Steam CEG" style DRM (where a game could in theory run without the client whilst the .exe could also be locked to the motherboard that downloaded it and needs the client to handle any hardware change). "Portable games" are certainly not as simple as they used to be...

Maybe testing on the same PC but with a different Windows user will show whether it's tied to the user profile or hardware.

Something must be wrong with my copy of Speed Brawl then. I extracted the archive I made into a 64 bit wine prefix* and then tested it.

With no parameters the title screen comes up and it sticks

With -EpicPortal the title screen comes up and it sticks

wine ./SpeedBrawl.exe -AUTH_LOGIN= -AUTH_PASSWORD= -AUTH_TYPE= runs the game fine.

* I am a linux user, I have the epic client in a win 8.1 virtual machine with no drives from the host. I download in the VM, run it from the client, close the client run it without the client running to check 1st time, then scp to my linux box to check in wine and if necessary proton.

You might want to add the infos about online capabilities and/or savegames to some games.

For example: Yes, you CAN play Death Stranding without launcher, but the savegames are not compatible.
Also without the launcher you won't be able to see other player's packages, roads and constructions.

Also the Sinking City works without launcher, my command line is:

"<Installfolder>\TSCGame.exe" -epicapp=MiddleMist -EpicPortal -epiclocale=en

(the last option sets it to english, otherwise it uses the desktops language setting)

For this particular game, I actually found a way to transfer my Steam save data to the DRM-free Epic version, but it for the life of me, I can't remember what I did. If I remember, I'll post it here.

So you tested on Win 8.1. which would confirm Grargar's theory that this trick simply does not work with Win 10.

How are you sure the steam version won't require the account?

I'm sure it will require Steam account. The difference is that the Steam client and all of the games that only use it as DRM are completely portable. You can put Steam into Offline Mode and transfer everything to literally any number of PCs that you want to, and you'd never have to go online again before being able to play all of your Steam-DRM-only games. You can't do that with the Epic client.

As long as there's no extra DRM, Steam games are playable offline forever. You just need to back them up once each, along with the client.