21% is VERY dry and that level makes your guitar very susceptible to cracking. Do yourself a big favor and buy a good humidifier for your whole house.
I use Hercules stands - I use them mainly for my odd-shaped guitars like my Gibson Firebird and Flying V that don't sit comfortably on conventional stands but the stand would work just as well for acoustics plus it has a locking grip that holds the neck.
I was like you, fretting over the built-in tuner. Then I realized you can get a great soundhole tuner like this one: https://www.amazon.ca/dp/B018K9K034/ref=cm_sw_r_cp_apa_i_xdpgFbFRNTX5Q
It works perfectly, is tiny and discreet, and now you can truly focus on what's really important - the quality of the guitar itself which is what affects the tone, not some extra electronics that do not!
What did you end up doing?
I’m in Oklahoma. Weather varies but it’s usually pretty humid. I keep my guitars hanging in my office and I have this running if it’s humid. It does a fantastic job keeping the humidity level at 50%.
Yeah that humidly level is pretty high. I’ve learned from experience that to see any noticeable difference with humidity in a room/home you’ll need a heavy duty dehumidifier. I use this one in my office/guitar room and it works great. I can set it to a specific humidity and once the desired humidity level is reached it shuts off.
I use these, one under the headstock and one in the sound hole for both of my Martins. They regulate the humidity in the case. They absorb moisture when humidity is high, and give off moisture when humidity is low. Keeps it at around 40% in the case.
Get a hygrometer to put into your case to monitor.
Have it looked at by a luthier. I have a Gibson acoustic from the 1960's that has that, but it's also 50+ years old so I would be concerned if it was a guitar less than 10-15 years old. BUY A HUMIDIFIER! High end guitars like that need to be kept around 55% humidity, I believe. The wood will take in and release moisture, which over time can warp the wood unless you're humidifying it properly. This is the one I use:
You should buy a small humidity sensor to keep in the case with the guitar and/or in the room with the guitar. Don't trust your humidifier is putting out enough or too much. Govee makes some for $15 that connect to an app on your phone. It could take weeks for the guitar to respond to proper humidity.
For the room: https://www.amazon.com/Bluetooth-Temperature-Thermometer-Hygrometer-Calibration/dp/B07DWMJKP5/
For the case: https://www.amazon.com/Govee-Thermometer-Hygrometer-Bluetooth-Temperature/dp/B07R586J37