cats-blender-plugin VS pxMaxScript

No problem! Also, i recommend you install the CATS blender plugin, it is intended for VRChat avatars, but it can atlas your textures, fix some armeture issues (or cause them) and generally makes humanoid creations easier to make, here’s the download link: https://github.com/GiveMeAllYourCats/cats-blender-plugin

Are they MMD models? If so you can get Cats Blender Plugin which was made for porting MMD models into vrchat, which runs off unity. So it's really useful and saves alot of time in blender. Even for actually developing a game I'm pretty sure this will come in handy.

For blender here is the download link for the add on which lets you convert the vrm file into fbx, you can convert it back to vrm on unity. https://github.com/GiveMeAllYourCats/cats-blender-plugin

You can use the Cats blender plugin for that https://github.com/GiveMeAllYourCats/cats-blender-plugin

As for example, this exists in cats blender plugin which can optimize for Quest or Desktop without much effort needed by the user and with decent results. https://github.com/GiveMeAllYourCats/cats-blender-plugin/wiki/Bake

If you own the model, there's always...

If you are converting it, it's likely the VRM-named bones are converting too, which renders its old animations useless. If you convert, new animations might need to be assigned. Try using CATS Blender plugin if you haven't already, for reassigning blendshapes.

It didn't get much attention earlier, but the Bake panel in Cats will take any avatar and turn it into 1 mesh, 1 material, 32k tris exactly in two clicks (or 5k tris for Quest). I still need to add options to produce multiple seperated meshes/materials for more varied Desktop use, but it's what I use to make my avatar Good-rated.

I did a script that may help to close holes progressively with mostly quads and few triangles. See on my github.

You can get it from Github: https://github.com/piXelicidio/pxMaxScript/tree/master/PolyPainter