Vratislav

In general, new worldgen (rapids, berry bushes, dungeons) will activate in unexplored areas. Not sure about fish. In already explored areas, you may try to replace standard streams by rapids in creative, I'd not consider this a big cheating. You may also try to regenerate chunks (at least these that were not touched) or prune the world for untouched areas to be generated again, but this may be risky and create terrain walls on border chunks, especially if using worldgen mods. So to make a backup the world is necessary. (I have bad beginner's experience with regen when upgrading to 1.21 with red clay came and I was so eager to generate red clay deposits that I run to it without making backup, forgetting I use Plains and Valleys mod, so I created really ugly chunk walls quite nearby my base. Then I spent hours in creative by masking them as natural cliffs .)

As I have tried to play in pre- releases and testing mods I use in my long time world, yup: there were a lot of changes under the hood, and mods that are not updated will mostly cause problems. For the most popular mods with dedicated developers, they will surely update to 1.22 stable soon and we should be deeply thankful to them. For other cases, I can recommend from my experience mostly with worldgen mods: Check if the latest version of the mod was updated at least to 1.22-pre 8/10 version. Woldgen mods from 1.21 will surely not work correctly, even mods updated to pre- 4-5 version may fail as the worldgen was modified due to elements like berry bushes and dungeons. Some mods that are no longer being updated, could be forked and are maintained by other people, e.g. Natural Trail Mod has at least third fork already. If you are able, the abandoned mod is simple and the fix is possibly easy, you may try to update it for yourselves (not that I do it, but there are many players who are capable of it.)

But I was not able to replicate in .rc.10...

It did not compensate?

As there are problems to use the schematics in later stable versions: The schematic was generated in version 1.21.5 and the worst offender of problematic blocks is probably Natural Trail mod CUPdated, that I am not fully sure with version used. But it should be either https://mods.vintagestory.at/trailmodcupdated 1.2.1 or rather its 1.3.0 fork Natural Trails updated here: https://mods.vintagestory.at/show/mod/29192. I will generate new version of the schematics after I successfully upgrade the world on 1.22 stable.

It seems that "symmetric" layout (water from the top to the middle or all 8 covered) means that the wheel cannot decide, where to rotate and how to calculate the output. Seems logical. However, I was surprised that the relation of the number of active blocks and of the output is not linear.

Have you checked number of active block powering the waterwheel? I did some experiments earlier to realize that "low water" has usually 3 active blocks, but with high water, you may get up to five active blocks powering the waterwheel. However I haven't tested for the difference in power output.

Yes, most advice was already said: Starting from small and expanding slowly, leaving enormous detailing (and chiseling) for later, designing in creative, (ab)using MC tutorials and using real buildings, MC builds or even builds from other games for inspiration. In addition to this, I'd really emphasize designing, starting from rough paper sketches (paper with 5mm grid is your best friend) and then in more detail in creative. You may test general proportions of the building just by sketching it on the paper. Then, in creative, you set up colors and details: which local stones fit with local wood types, what is the good window frame design (by putting several ones put side to side), elaborate crazy ideas, and decide then if to build it. It can be tweaked in survival a bit, so even the creative designing does not need to be too meticulous. From my personal experience, in two 1.22 testing worlds, I was lazy to do the design on paper or in creative and started building bases without designing: oh, I was disappointed with the results...

There are actually some mushrooms that are slightly poisonous when raw or cooked briefly, but perfectly fine if properly processed. So it should depend on the realworld behaviour.

I know the place and I did not explore it happily.

Are they synchronized?

This will be feat and I am very interested! (Also, greeting from fellow Greek temple builder, despite in TOBG. I tried Artemida's Epehesus temple. The construction was easier, of course, as I had to fit to the whole block column sizes and distances, but the result was like 95% close to 1:1 so I was satisfied.)

And this is the core of the problem. The grow speed should be at least some kind of continuous function to reflect the worsening nutrients conditions, not containting these jumps that simply double the growth time for last two stages. Then the growth speed would decrease step by step and the lasting of the next stages would be more predicable. I have made some wild assumptions and did not bother to find exact numbers, so do not take following table as valid. It is possible example of crop stages on medium 75% moisture, in current model and if we do not decrease growth speed from 58% to 29% when the fertility decreases from 20,1% to 19,9%. If the speed was distributed more evently the long growing crops were less exposed to the risk of prolonged last 1-2 phases.

Well, the stability itself is not bad, but as other say, there is a bit more bugs than is acceptable for smooth gameplay.

I also confirm bugged traders in 1.22-rc2. I have this experience in one PC. I got some "asset XYZ not loaded" warnings in the loading screen, then traders did not appear in their outposts. In other PC, I got the traders appearing in rc2 just fine. The problem might be caused by stacked installation of several pre- and rc- version to the same spot without full removal of the previous ones, as I did this without care with aforementioned result.