I am using Site Collection App Catalog. Can I upload New Upgrade package to it?

Yes, you can.

Related articles:

• If I have multiple site collections and one of them is using Site Collection App Catalog, can I test the new package on it before installing on the entire tenant?
• I cannot test the new release on the site collection that uses Site Collection App Catalog? What for can I use it then?
  

Main articles about New Upgrade:

• ShortPoint SPFx New Upgrade for Office 365 and SharePoint 2019
• ShortPoint SPFx Auto Upgrade Feature
• ShortPoint SPFx Sandbox Mode Feature

You may check other FAQs about ShortPoint Upgrade in this folder.