you can use a hygrometer. 22° is a crazy cold setting - way too cold and to dry if you can actually get your room down to 22°C. you need to set the temp and humidty to a comfortable level and not chill down because you can. then when you go in and out you will get sick.

that is why you want to use dry mode with a higher temp setting. you can adjust until hygrometer shows 55-65 % humidity. room will feel cool and comfy then. there is no need to go down to 22° to begin with and that will cause you problems also if you leave the house due to the higher temp-difference.

which is why dry mode @ 28/27 is working. its dry and you wont feel stuffy. no harm done - try for yourself.

maybe your room has too much airflow? or the aircon didnt suck enough moisture. did you check the humidity level? if you can get the moisture down to between 50-65% you should be comfy though 65% is bordering it. of course you need a rather sealed room as outside has high humidity levels when its not super hot. best controlled with a ventilation system. our house is completely A/Ced this way, fresh air coming only from aireguard fresh air system & bathroom and kitchen suction and the occasional door opening. proper door and window seals prevent humidity creeping inside. if like that you can effectively chill the house to 28° and hover between 45%-65% humidity at all times. That feels pretty comfy and as added bonus you dont have any issues with fungus or mold (too dry). but then mileage might vary. i think you might also need to control airflow to make this really work.

I wonder how accurate is the reading.

Cause this kits make it as hobby/DIY/project. Doesn't require accuracy as long as it cheap for hobby.

So I have this impression that this kits are not accurate.