Ive actually noticed this happening for quite awhile. My theory is that every biome type that I disable by setting weight to zero, gets replaced with red woods. I think this is the case because the more biomes I disabled in testing, the more red woods would appear.

Also, the vanilla desert biome becomes super rare, even when I give it a very considerable weight.

The tropical islands doesnt seem to spawn anymore either. Ive not seen one spawn in testing since MC version 1.14.4

Im also not seeing orchards. Ever.

I test biome spawning by setting config to tiny/small and exploring each world a bit to see if I need to alter biome weights.

Biomes are determined by the climate. If you’ve disabled every other biome in the climate except for Redwood Forests then what you’re describing is entirely expected behaviour

And which biomes are grouped with red woods? It would help if we could see what biomes are grouped together in the config.

Jade Cliffs and the Woodland

Plains are also in the same climate.

"Im also not seeing orchards. Ever."

They're a sub-biome of the vanilla Plains, so if you disabled that, you're not going to see them.

Jade Cliffs and the Woodland

• vanilla plains

That seems like a pretty small list for a climate group.
Just a bit of feedback that might be useful to you in grouping climates-> I disable the vanilla plains because you added similar biomes in bop. Prairie and meadows, plus their sub biomes. And orchard, whcih I never see since its linked to plains. I also disable vanilla mountains because bop adds several high altitude biomes. Same for vanilla swamps. Bop adds lots of swampy biomes. And I prefer using bop biomes over vanilla ones. if you had a desert and savannah equivelvant, i would disable those too. Vanilla forest type biomes as well, I disable because I like the bop ones better.

I think nice feature to add, would be a true/false toggle for vanilla biomes, because id rather not use them at all. And if setting their weights to zero is mucking up the climate groups... well that is a problem.

The climates are balanced around having all biomes enabled. Our biomes aren't meant to replace vanilla biomes, and we can't really do anything about balancing if you're disabling half the biomes in the game.

Well they do a good job of replacing vanilla. Consider adding the toggle. Alaso consider that people might also be adding other biome mods, and maybe dont want any boring vanilla biomes at all.

A toggle for what? You can already disable them by setting the weight to 0 like every other biome. I mean, you already said you had them disabled, so I'm just not sure I understand what you're even asking for.