Magisk encryption and update + Galaxy S9 Plus?

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I have MagiskSU installed on my Galaxy S9 + G9650, and I wanted to know what is the use of the option: "Keep forced encryption", even my phone is encrypted, whenever I call I have to enter the password to decrypt and when trying to access my data via TWRP, nothing appears. Will this option help me with anything? Another question, if I have to update Magisk, how do I update it on my phone since it is encrypted?