Is there any possibility to make an FPS view on portal templates , like a first person perspective without the avatar present on the scene ?

Yes!

1. Go to the hamburger icon in the top right
2. Click Space options
3. Click movement
4. Click add+
5. name it “first person” (or whatever you like)
6. Toggle on force first person
7. Click the back button (return to the “movement” tab)
8. Click on the “current movement profile” dropdown (currently most likely it is set to “default”) and set it to your new movement profile