Have received official feedback from Samsung via Digitec:

"Our responsible department has gladly reviewed your request and contacted Samsung. They informed us that the Samsung TV (release year 2020) supports the following HDMI 2.1 functions:

- HFR (High Frame Rate) 4K@120Hz
- HFR (High Frame Rate) 2K@120Hz
- 4K@60Hz
- VRR (Variable Refresh Rate)
- Dynamic Metadata
- ALLM (Auto Low Latency Mode)
- eARC

However, it should be noted that the following HDMI 2.1 function HFR (High Frame Rate) 4K@120Hz is only available on HDMI port 4 and eARC is only supported on HDMI port 3. All other HDMI 2.1 functions listed are supported by all HDMI ports." End of quote

Thank you for your message. But as I said, there is no mention of HDMI 2.1 anywhere. Not even in the Samsung manual. So I have to assume that Digitec misled me with the wrong information.

Thank you for your answer. Not even the Samsung manual says anything about HDMI 2.1, so I assume that Digitec has deceived me with incorrect information.

Ok. Thank you for pointing that out. However, it is not mandatory that eARC requires an HDMI 2.1 connection. According to research at https://hifi.de/ratgeber..., it is also possible with a firmware update.
Therefore, why is 4 x HDMI and 1 x HDMI 2.1 mentioned in the specifications?

The HDMI 2.1 is labelled HDMI earc. I had to google it briefly, but in the end it means the same thing (no earc without hdmi 2.1).
The HDMI 2.1 can also be used for devices with the old HDMI, which is why the TV only has 4 HDMI connections, which means 4x HDMI and 1x HDMI 2.1.