As it's not fully clear to me: the Reforced version is just Spellforce 3 improved, and not any of the other Spellforce 3 games, right?

As far as I can see then it's just an 'upgrade' / revised version of the game and it does not contain any DLCs by itself.

Take a look at the Steam pages ! :

https://store.steampowered.com/app/311290/SpellForce_3_Reforced/

https://store.steampowered.com/bundle/8177/SpellForce_Franchise/

P.S.
To my great dismay I can see that it would be EUR 12 cheaper to buy all the Spellforce 3 on Steam if one have the previous Spellforce games and buying the "SpellForce Franchise BUNDLE" .
Ref. :
https://store.steampowered.com/bundle/8177/SpellForce_Franchise/

GOG have an offer on the Spellforce series but it gives you no extra discount if you already have the previous games :
Ref. :
https://www.gog.com/promo/spellforce

Actually I saw that I have Reforced in my library.
But when I check the corresponding page in the shop it is not marked as owned.

I have the same issue.

There appear to be some issues , maybe it is something that GOG needs to work out or fix . Some people also appear to have issues installing using Galaxy !

https://www.gog.com/forum/spellforce_series/spellforce_3_reenfored_edition_appears_in_game_roster_but_cannot_be_downloaded

"Spellforce 3: Reforced" is for the most "Spellforce 3" with the additional engine improvements that the two stand-alone sequels in the serie already had, so to pass all the good things of them to the original one.

Some game dynamics also are changed, and while they where at it they added some more contents.

The issues that GOG is having with the game are comprehensible, because they must "substitute" the original game, without achievements, with another one that needs more functions, while putting the previous main game in the Extras of the newer game...

It's a pretty mess of data to be managed, and moved around.

Another issue I see, seems to depend to a wrong upload to GOG from the devs, because it contains some Steam libraries, that obviously shouldn't be there.

The GOG game page says nothing about "the need of Steam" to run the game, that naturally will be an unacceptable situation.

So it is only a matter of time, just leave GOG to resolve the database issues of moving those two games around in the same profile, and wait for the devs to correct the package sent to GOG.

They could have just waited to sell the new game AFTER all the stuff was ready, but well, it would have been too easy... :P

I have only Soul Harvest in GOG. It did download 150MB today when I forced verify/update, but it still shows August 2020 release on main screen. :(
I was looking forward for game controller update...