Excellent question!

The longest wavelengths of light are generally classified as "radio".

So radio telescopes have been tasked to explore the very early universe.

https://en.wikipedia.org/wiki/Reionization

If I understand it correctly, the "Period of Reionization" is first light we can see from processes like stars and galaxies.

There was ionized plasma at the beginning but the universe was like a really thick fog everywhere, and that first light was scattered around and you can't really see stars. As the universe expanded, that fog cooled down, and you could see, but cold matter doesn't emit much light, so there wasn't much to see. It took a while for gas clouds to collapse into the first stars, heating up the gas to ionized plasma once again, so it's re-ionized matter.

The Low Frequency Array, LOFAR, has been used to study this "Cosmic Dawn".

The Square Kilometer Array was designed to explore this era.

But! Not a radio telescope JWST has revealed unexpected, huge globs that seem to be galaxy-sized gas clouds collapsing into (maybe) black hole cores; the thermal emission from the collapse isn't nuclear fusion, so I don't know if those are "stars". But it's very early light.

Honestly, every time a new class of telescope is built, it discovers fundamentally new phenomena.

https://duckduckgo.com/?q=LOFAR+square+kilometer+array+reion...

https://news.ycombinator.com/item?id=44739618

https://news.ycombinator.com/item?id=46938217

I searched "Reionization" and "Cosmic Dawn" plus some favorite telescopes via web and here using the Hacker News search (Agolia).

(Certainly you know the difference between radio and infrared, but I had to look into how those choices of telescope have observed different aspects of Reionization Era, got nerd-sniped, and just had to write it down in a couple of sentences.)

A Cosmic Miracle: A Remarkably Luminous Galaxy at z=14.44 Confirmed with JWST