CDMA iPhone using GSM

An iPhone SE 2020 should support modern cellular networks. There really hasn't been a dedicated CDMA or GSM only iPhone for a long time now. On your iPhone currently you likely are using LTE, not CDMA, which hasn't appeared on an iPhone since iPhone 5.

So, to answer your question, you really don't need to be concerned with GSM or CDMA. And yes, iPhone SE 2020 supports eSim.

You need to contact your carrier if you are not getting a good cellular connection on your iPhone.

That is a GSM phone. The only CDMA only model was a version of the iPhone 4 sold for use on Verizon or Sprint.

There are no longer any supported CDMA networks on the planet.