Private DNS provider

Hello community, I am newbie here.

I have issues on my Xiaomi redmi note 9 pro (Android 11)

i am using Faster & Safer Internet app on my phone. I selected Private DNS Provider with host name: and saved.

At home my wifi have connection to internet very well. But at my work wifi can not connect to internet. I also can not use my mobile data too. broswer apps not working Mozila and chrome. i can use youtube messenger etc except that browsers.

i wanna have that DNS to be safe because mobile data is sensitive for me.

maybe both app and that DNS is not recommended right?

any solutions please. thanks.