After reading the Paradox Forums and the Steam Forums, it's clear that the 'hotfix' for the game is anything but a fix. The 'hotfix' only half heartedly partially fixes some in game bugs, and ignores a large number of the rest of the bugs bought in with B&B.
There is, supposedly a second 'hotfix' in the works by Paradox. There is still no word on a proper bug fixing PATCH. Nor are Paradox, or the cause of the new bugs, abstraction, willing to allow users to do an in-place roll-back on Steam, or allow the download and install of an older working version of the game on any platform the game has been released and sold on.
GOG users who have the full set of installers for older patch versions of the game are at a massive advantage here. Basically, the sole solve, to get an, at least working game, is to uninstall EVERYTHING of the current version, install an older version of the game from scratch, and not let GOG Galaxy update the older version re-installed.
In my GOG installers archives, I have the installer sets for Evans (249143), Tito(1001551), and Piazzi(1007783). I know Evans works so I can reinstall that, and have a properly working game. For me, Tito broke rocket launches to and from Mars, so no way I'll use it to reinstall the game.

Thanks for the answer. So the alternative is to wait for another fix/patch. By the way, I don't have a B&B yet. What I know is that the rocket launch after the patch, which has also brought free stuff, did not work with me and even then not the planing. The fix from the 13th has at least fixed the rocket launches. At least with me. It is therefore feasible to play without the leveling function but many Stelllen can not be built thereby, just domes are there bitchy. I think I'll wait for now, at the moment I do not have so much time anyway^^

The Free Update released at the same time as B&B, means that everyone gets the same base game bugs. B&B puts the bugs in, as well as ones specific to B&B. The free update puts the bugs in as well. And the hotfix released earlier this week only fixes a few of those bugs, and there's supposed to be another hotfix being released early next week.
Steam Forums thread: Hotfix #2 arriving on Monday!
So basically at present, we STILL have a broken game, that can only be rendered base game playable, if you have the set of installers for the Evans (249143) patch.

Proper ground levelling has only worked with Choggi's mods for the Evans (249143) patch. The Tito(1001551) patch broke that functionality of the mod, and it still isn't fixed for Piazzi(1007783).
The way the ground levelling works in stock SM, is it creates a shallow ramp on the border hexes of the levelling tool, with the surrounding ground areas, the inner areas once the tool is larger than one hex are never fully levelled to exactly the same no matter how many times you use the tool, and that causes supposedly levelled ground to be and remain Uneven Ground. There has never been an official fix to that long outstanding bug, to make the stock SM ground levelling tool fully and properly do what it says on the tin. Choggi's mod is the only thing which resolved that issue.

Okay interesting. Did not know that it is not actually wanted with the leveling of the floor. I thought if you place the surfaces exactly next to each other so that the honeycombs have no bend down, then that already fits^^ But yes somehow are always unevenness to see.
Let's see what the fix brings, maybe I'll look at the mod when it goes again. I'm not the type for building mods or something, rather take what the game officially offers, but the floor tool would be important that it works. If the mod then not(for me) adds more unnecessary.^^ Thanks for your answer.

So, with the new fix...it don´t work. I can not use the plane function. But also with older saves. With a new mission/a new profile it works. I would rather continue playing the existing save, but as long as the planing doesn't work there, I'll have to start over.