Question about Apple Mac Mini - Late 2020

None. I would only ask Galaxus whether the more expensive version already has the additional 10 GB Ethernet connection built in.
But it's only worth it if your home installation supports it at all.

I am not an expert on the subject. I already owned a Mac Mini (older model) and decided to buy a cheap new model. I was confronted with two models (2020) and decided to buy the Late 2020. I had to decide whether I wanted the model with the Intel processor or the new processor from Apple ("M1"). I decided on the slightly more expensive one (with M1). Thank goodness. The difference is huge in my subjective experience: performance and stability).

There is no technical difference, apart from the model number: the model with the model number ending in "SM/A" is a model for the Swiss market (and also the cheaper one), the one with the model number ending in "D/A" is probably intended for the German market. Here it makes sense to pay attention to price and availability.