What is the reason for high humidity in a home?

https://paylesspower.com/blog/how-to-lower-humidity-in-house/

https://www.abchomeandcommercial.com/blog/what-causes-high-humidity-in-a-house/

Where do you live? That may also contribute to your issue. I live in zone 9 in southern California where it is extremely dry, typically humidity is in the 10% range. My friends in other parts of the country have much higher humidity and all use dehumidifiers in their homes. Do you have your HVAC system inspected at least annually? Mine is serviced spring and fall. How often do you wash or change the filter? Mine is changed once a month. See if these help you pinpoint the source.

https://www.solencosa.co.za/blog-articles/lizelle-verrall/1/the-top-10-causes-of-high-humidity-in-your-home/52

https://www.abchomeandcommercial.com/blog/what-causes-high-humidity-in-a-house/

https://www.humidifiergeek.com/what-causes-high-humidity-in-house/

Do you have an a.c.? That would help alot.

There could be a water way under the house