Yes, you can play some games, including Astro’s Playroom, on the PlayStation Portal with PlayStation Plus Premium without a PlayStation 536.
Here’s what you’ll need3:
A PlayStation Portal.
A PSN account with an active PS Plus Premium membership (costs $17.99/month or $159.99/year).
An internet connection with a minimum of 5Mbps upload and download speeds (Sony recommends 7Mbps for 720p streaming and 13Mbps for 1080p).
To get started, update your PS Portal's system software3:
From the top right of your PS Portal's home screen, swipe left to see the Quick Menu.
Navigate to Settings > System > System Software
Select Update System Software
Then, enable the Cloud Streaming beta3:
Open the Quick Menu again and navigate to Settings.
Select Cloud Streaming (Beta).
Turn on the Cloud Streaming (Beta) toggle, which is off by default.
Once enabled, you can access compatible games using Sony's cloud streaming service3. Over 120 PS5 games are available via cloud streaming from the PlayStation Plus Game Catalog6.
Keep in mind that the cloud streaming feature is still in beta, and some features, such as game trials, party voice chat, the Create button, 3D audio, and in-game transactions, may not be available initially, but could be added later3.