learn how to bake and atlas your textures - doing this for a model can easily bring 200mb down to around 40mb - 50mb
for most models with "over 90+ toggles!!!" which seems to be most eboy/egirl models with more outfits than anyone actually uses on the daily, there are simply so many things on the avatar that just lowering texture sizes will not come close to being enough to properly optimize them (im just using this as an example pls dont hurt me)
the best tool for this, imo, is SimpleBake, providing the ability to both atlas textures and bake multiple textures to single images without losing much visual quality; pairing this with a UV packer, you can very easily get the coveted "1 skinned mesh renderer" that hyper-optimized avatars boast; of course it varies though - any optimization is good optimization!
realistically, many of these creators that throw in 2k+ textures on 30+ mesh renderers do not care about performance or optimization, as a result it is going to be that much harder to optimize those avatars
if you are willing to sit in blender and fix the egregious ignorance of optimization, it can be done; otherwise, decimate textures*, maybe even remove some of the things you feel you won't use as often, and look into tools like Polytool; your results will vary
* textures generally shouldn't be more than 1024x
, using DXT1
compression (not crunching)
maps (roughness, metallic, etc) can go even further down to 512x
, also DXT1
even further, cubemaps and matcaps can go down to 256x
or even 128x
if it does not affect the overall look as much
normal maps are the only thing that should ever be at 2048x
, and sparingly, using RG compressed BC5
instead of DXT1
, you can also use BC7
; in some cases this can look better but DXT1
has a higher compression ratio due to lack of the alpha
channel - most textures and maps are not transparent, but if they are, try BC7
and the final note - don't be afraid to use Bilinear
instead of Mitchell
when compressing; Mitchell
is great but does blur finer details while Bilinear
tends to be more sharp at lower resolutions
there aren't any real good guides around but I do believe I've got a few good tips to give out - feel free to yell at me for more