You likely have a Safari instance opening in slide-over view.
To eliminate this, first pull down on the grey grab bar at the top of the Safari view - transforming the view into a split-screen view. The split-screen view has a central divider, upon which is another central grab bar; drag this all the way to the edge of the screen.
You should now have restored your expected functionality. I recommend that you review the iPad User Guide for iPadOS to learn about multitasking in iPadOS. Here is a link to both the downloadable and online versions of the User Guide:
https://support.apple.com/en-gb/guide/ipad/ipadf3dbb83f/ipados
Here is short video that you’ll doubtless find informative:
https://youtu.be/nSBZKr5kXYM
I hope you find this to be helpful in fully resolving your problem.