No, you cannot. You need to disable the Auto Upgrade first, and then you will be able to upgrade to Beta.
Related articles:
- Can I preview the Beta version?
- I use Sandbox Upgrade Mode. If I have both public and Beta release, can I preview both versions?
- I am currently on Beta version, and the new public release is made. How can I go back to the public release?
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.