well... if you go by the ergonomic standard you should be sitting upright with your arms at 90 degrees and type without resting your arms on anything. however, that just is not practical in the real world. kudos if you can manage this. typing on a desk that is too high and raising your arms above the keyboard though, is not the ergonomic standard. any long term keyboarding will damage your joints and tendons. take frequent breaks and stretch once in awhile to help prevent such things.
i use a desk that is about an inch too high and i tend to rest my forearms on the desk but my wrists are normally elevated. i prefer to use mechanical keyboards but have a cheap freebie dell keyboard at work i am thinking about replacing.
i've been using a keyboard for over 15 years and yes, i can notice some slight issues. if you use a keyboard every day there is no escaping it. look at any other daily activity and see how it affects the body. you can do things to help prevent it but ultimately most everyone experiences some sort of problems eventually. they do not have to be major, depending on your habits.