JuicyOrange

You completed the main story before encountering Mewtwo. Necroflame encountered it after assignment 5 and got it as a mid game legendary as intended. Young Mewtwo is the default encounter and the lore explanation for you encountering normal Mewtwo was that during the course of the story it matured.

You can take young Mewtwo to a hidden room in the cerebral complex to make it mature.

Alright. Should be ready to go again. Simply replace the old save file with this new one. Just as a reminder, which I assume you've done already, but please make sure the latest patch is installed to remove "the rock". Apologies for the inconvenience.

https://drive.google.com/file/d/174pxY1JtMmsrUb3ZlYR2MMMHmCwKT_C1/view?usp=sharing

Here are the instructions to get started.

Firstly you'll need to find the save file.
Type "saved games" into the search bar on your computer and navigate to the Pokemon Void folder. Copy the Void.rxdata file.

Next you'll need access to a media sharing platform such as google drive or mediafire. Using the service of your choice upload the save file. This site doesn't allow for direct sharing of files to my knowledge.

Once uploaded, right click the file to generate a shareable link. Afterwords share the link here I can do the rest.

I'll try to get is back to you ASAP. It shouldn't take long.

If you have any troubles let me know and I can assist as best as I can.