Steps to replicate:
1-Within any CPT settings, open Settings>Custom Fields tab and select File Upload field from the standard fields section.
2-Set the file upload limit to 0 for unlimited uploads. Save then reopen to check the value saved in that field.
3-As a non-admin, creator edit an instance of the CPT whose settings you just changed. Check the message displayed on the file upload field. Attempt to upload more than one file.
Expected results:
1-As admin: When you reopen the file upload field, you should see 0 in the file upload limit field
2-As non-admin, when you edit a CPT, the file upload field does not say: “You can upload 1 file”.
3-As a non-admin, you should be able to upload more than one file.
Actual results:
1-As admin: When you reopen the file upload field, you should see 0 in the file upload limit field
2-As non-admin, when you edit a CPT, the file upload field says: You can upload 1 file.
3-As a non-admin, when you attempt to upload more than one file field says: “You have exceeded your file upload limit of 1 file”
Using a value of 500 instead of 0, the expected and actual results match.
Other details:
GD version: 2.0.0.81
WP version: 5.3.2