The attached-file size limit is ~4Mb - so ZIP them if necessary.
Direct attachment of SKPs is allowed but if you upload a SKB it needs to be inside a ZIP anyway, as there are only certain types of files allowed for direct uploading...

Zipping will optimize the file size uploaded...

I know you can't purge the SKP because you can't open it 😒 , but bear that in mind for the future.
A SKP can shrink considerably when purged in Model Info > Statistics...