@Mytoast Admin,Thanks for posting in Q&A.
For your issue, I have done some research, here are some information you can check.
1.This feature is in public preview.
2.There are some limits:
- A maximum of 20 ADMX files can be uploaded. Each file must be 1 MB or smaller.
- For each ADMX file, only one ADML file can be uploaded.
- Each ADMX file supports one language.
3.Currently, only en-us ADML files are supported.
4.Some ADMX files have dependency prerequisites.
Here are some links you can refer to fix this error.
https://www.anoopcnair.com/intune-admx-file-upload-error-referenced/
https://call4cloud.nl/2022/10/the-school-for-admx-import-and-evil/
Non-official, just for reference.
Hope above information can be helpful.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.