You can try this:
Press Windows + R
Searching appdata
C:\Users\youruser\AppData\LocalLow\VRChat\VRChat\Cache-WindowsPlayer
Open a folder
Change the data name into: name.vrca
Download AssetRipper for your system
https://github.com/AssetRipper/AssetRipper?search=1
When the program is installed click File
Open file
Open the .vrca file
Export all files into a folder
Create a new unity project
In the assets right click
Show in explorer
Import the files within your asset folder into the unity asset folder
Let everything load
Drag the blue box into your Hierarchy
From here you'd upload it but that's where I get stuck personally as the VRC SDK gets removed.
Edit:
This might just be the avatar I tried but I don't feel like trying anything more tonight.
I think it has to do with missing scripts.