How to prevent porn?

So I managed to switch to this DNS and it blocks everything which is good, my problem is that I did it on my computer, not router which doesn’t have that option and my brother uses the wifi too.

I created a new windows 10 account without full control, so when I log in to that, I need the admin password to be able to change the DNS, install or delete things, etc.

I figured I can just create a new random admin password, put it in a piece of paper and keep it at another location, at work or simply send me an email to my future self in 6 months or 1 year with the password, that way, the admin would still be there, but I won’t able to change things, including the DNS with my guest account. Of course, I don’t want to lose admin rights and I’d rather have control and just block access to DNS on guest account.

Is there a way to create a guest account which can still delete, install programs but not be able to change the DNS wifi settings on my PC?

Ultimatetly I may have to build this guest account as best as I can with the programs I want and then just store the admin password somewhere else or future.me the password in 1 year