Are there new handhelds in that form factor ?

Like every other week.

Well, not really, but there's a constant stream of new consoles from Retroid, Anbernic, AYN, Ayaneo, Miyoo... and a dozen other brands, and it's kinda an in-joke.

Some are in a PSP-like form factor, Vita too, even PSP Go, some are like a GBA/GBA SP, Game Boy, DS/3DS... and some come in unusual form factors. Some are cheap in components and build, others are really powerful and well made (what is reflected in the price difference). All options/preferences are covered, I think.

Just have a quick look here (no need to watch the videos, just skim through the thumbnails to see what's going on):

https://inv.nadeko.net/channel/UCoZQiN0o7f36H7PaW4fVhFw

You'll find a few interesting PSP-like ones in the second and third page, but going further maybe the models are "too old" or discontinued.