Apple has removed the startup chime from all the Mac models starting from Late 2016.
About Mac startup tones
Mac models from early 2016 and earlier make a chime sound when they start up. Mac models from late 2016 and newer don't have a startup chime, with the exception of MacBook Air (13-inch, 2017).
Hyper-Threading is not offered by this chip?
Yes. This chip doesn't feature Intel Hyper-Threading technology.
Hyper-Threading is disabled by default by Apple now
This chip really has only 3 cores, and 6 virtual?
This chip has 6 physical cores.
Out of all the variants offered by Apple, Hyper-Threading feature is available only in the 3.2GHz 6‑...
Hyper-Threading is offered by some models of CPUs in the 2018 Mac Mini. The base-level 3.0 Ghz Core i5 does not offer Hyper-Threading however.
I'm writing this on a 2018 Mac Mini with the 3.2 Ghz Core i7 CPU - and it does indeed display 12 graphs in Activity Monitor indicating that Hyper-Threading is enabled and used.
Apple says: RAM is not user-installable on Mac mini (2018)
While I do not know what this means in terms of voiding the warranty…
Apple does not consider the RAM in a Mac mini (2018) to be user-installable.
The Apple Support page Upgrade or install memory in your Mac mini says:
Mac mini (2018) does not have user-installable RAM. You can ...