is there a way to run this pi-hole on cloud so, multiple users can use it , and also while using mobile data ? also, for those who do not want to spend on / does knot know to fiddle with RPi.

This should only be done in combination with a VPN. Open DNS points are not generally recommended

Check out nextdns instead. It can likely do what you had in mind

thanks. I will check this out.

is AdGuard also a similar approach ?

https://adguard.com/en/welcome.html

https://en.wikipedia.org/wiki/AdGuard

I know adguard has a pihole like thing called adguard home. Don't know anything about it beyond that.