This is my understanding from parenting & reading. If a child reaches 18 months and does not connect two words at all, ever (such as "what's that") then the doctor should do a little assessment screening. You should also look for a child to be able to attempt to look a direction that you are pointing. They should notice if other people are turning their heads to see something & also turn. If the child can hear the microwave, that doesn't mean hearing is okay. I am not saying there is a hearing issue, but hearing issues are generally not in a range of perfect hearing or total deafness, you get a lot in between & if a child has something like fluid collected, they get a muffled version of sound, but they hear. It still can impact speech considerably though.
So for me, I just see the doctor. The reason being, that if there is something wrong (and there very well may be nothing) you want something addressed on the sooner end of things. A lot of what you are saying does not sound concerning, but it's impossible to say without a full picture & that is something you can only do in person.
If you live in the states & do not have insurance or cannot afford an appointment, contact your local "Early intervention" program. You should qualify for a free assessment on speech & development. Many times, if a doctor is concerned, that is where they refer you to for your next step anyway & in the area I live, you do not need a doctor's referral to go straight there if you wish to. If I knew where you were I could give a link, but you can google it pretty quickly & find your local offices, again in the USA. I am not sure what services are done in this case in other states. I can also tell you that for me, a hearing test yearly is paid for on my insurance as long as a child is either not speaking at age level or has been referred by failing a hearing screen. I have had 2 late talkers & I did get their hearing checked several times just to ensure there were no physical barriers to speech.
All of my kids were seen at 18 months for a regular check up, as per the typical schedule. Were you seen then? Did you bring these things up? If not, then again, that would be my first stop. Like I said, none of it sounds terribly worrisome to me. Even for him to not do as asked (like dance), even though he did before. Many times a child can go through phases where they care more to do something & then tire of it, and won't respond. But again, it can be a normal thing or it can indicate something that needs work. A professional is absolutely able to determine if it's normal. I had a child that walked for a week & then stopped & went to crawling only, wouldn't even stand. I took him in. It was fine, but it helped ease my mind considerably to have him checked out & find out that it's okay. I am so glad I did too because it was still 2 more months before he walked again & I would have been worrying over nothing.