Is it possible to downgrade to v1.0.2.8 or older?

Should be, yeah. Haven't done it with Hollow Knight specifically, but if you're using Galaxy:

-Click on the game in the side bar, should take you to a page that says "Play" in green and next to that is a "More" drop down menu

-In the "More" menu, go to "Settings"

-in "Settings" there should be a list of "Override Features" including Auto-Updates

-Uncheck the "Automatically update to newest version" box, that should make a list pop up of which version you want to revert to.

This does provide "some" of the previous versions, but not the versions i'm wanting.

Unfortunately you cannot downgrade the game any further if you haven't backed up an offline installer that was released at the time. Even Galaxy only stores the latest versions of the game to give the possibility to still play a game even though an update has broken the game. Storing every version for every game indefinitely would just be too much to ask.

Why do you want to downgrade the game?

No it's not. Steam does it. Because i speedrun Hollow Knight and need different versions of the game for different skips and glitches.

No, Steam does only give the POSSIBILITY for publishers to store beta releases. Steam has auto updates and therefore offers a beta branch for publishers in case an update is breaking something. However this still is hardly used. I don't know how much this is used by Team Cherry since I don't own the game on steam. GOG stores several old releases for EACH game by themselves.

WRONG!
I don't know who you think you are, but you should really know what you are talking about before you open your mouth.
Just because you think you are right, or that you know something, doesn't mean you do.

Here's a guide on how to downgrade/install all version of Hollow Knight that's been released on Steam
https://www.speedrun.com/hollowknight/guide/yl0m6

You want to know who I am thinking I am? I think that I am a person who is able to post without being emotional and start shouting at people. You asked a question people were responding and you are now starting to shout. Well - good luck then with your help because I completely lost interest in helping you. Bye.

Good!
Because you are no help what so ever.
You gave FALSE information about something you know NOTHING about.
So you threatening to not "help" me anymore is actually the most helpful thing you could do.

I gave you the informations I knew and I worded them accordingly. I said that publishers do have the possibility to add old versions which is rarely used. Steam itself does not give the possibility to download older versions for every game. I also said that I don't know how the Hollow Knight devs have handled this.

" I don't know how much this is used by Team Cherry since I don't own the game on steam. "

Just because there does seem to be a workaround using the steam command line in the case of Hollow Knight does not change the fact that normally people are not able to rollback their game versions using the regular client. That's not a false information and in any case it was not even the information you wanted. So ... it still does not change the way that you cannot rollback GOG games further then what GOG stored which was one of the first reply that was given to you here by me. Hey, I actually tried it myself to be sure.

But since you seem to think I don't know what I am talking about I guess it's best for both of us to end this here.