It may say that on the specs page, but I've never been able to get that to happen in the real world. I spoke with an Apple tech about the issue and he told me the only way to get 60 hz was to use the TB3-to-DP cable.
One possibility is that I got my mini before the recent refresh. Maybe the 2020 minis are capable of it.
The "new" [sic] Mac mini from 2020 is a Mac mini 2018. Same exact internals. The only difference is the base storage has increased. It's a Built To Order Mac mini 2018 with an SSD capacity bump without the storage surcharge. That's all. Everything else is the same. It's the same CPU, same integrated GPU, same graphics capability. There is no revved CPU part. There is no Mac mini 2020
My Mac mini 2018 happens to be a refurbed unit that I purchased a year ago.
Do you really think Apple would blatantly LIE
on their tech specs page (which hasn't changed since the model was first released)? Even all the footnotes for the benchmark stats quote tests done in 2018. C'mon, give Apple a little more credit than that. Sheesh.
I assure you that I am getting 3840x2160p @ 60Hz over an HDMI-to-HDMI cable on a system I bought in 2019.
Check your cable and your monitor settings. Make sure the latter is configured to handle HDMI 2.0 on the HDMI port. My LG monitor required no such adjustment and worked straight out of the box.
My hunch is that your HDMI cable is inferior and can't handle the higher bandwidth.