There is no way to manually generate a planet.
There are "planet creation" saves. Hower a savegame contains a lot of information about Events, Stratagems, Assets and Models/OOBs. So any old Plaent Save will include old bugs.
Sigh, I wish you could. This is the single thing I hate the most about this game. I just want to create the planet I would like to play on lol
I think it would be nice to be able to manually configure what you want, this can go both ways of making something easier or harder, although the later is much easier to obtain with random generation.
One thing that could be patched in, until greater freedoms of manually choosing parameters for planets, is the ability to manually save the world before choosing your backstory mode and what your government will be made up with, as currently that is the downside of sharing saved worlds not being able to configure those last bit of details to what you want.
If that is done then perhaps there could be a community repository of generated interesting worlds, along with an attached pdf screenshots of the generation screens for finer details. These downloads would have to have the game build version in the filename of course, as zgrssd pointed out these saves would have existing bugs of that version.