Can I connect an Arduino Uno Wifi to Arduino Cloud?
If you sign in to Arduino Cloud the very first thing it asks you is which board you are using. One of the options is the Arduino WiFi Shield 101. That is a shield that you can attach to any Uno-footprint board (including the Uno) to give it encrypted WiFi.

Another option is the Yun shield which turns your Uno into a kind-of Yun.

There are many many other "clouds*" that support Arduino, and many that if you are a reasonable programmer should be simple enough to make work with Arduino, since 99.99% of them all work through some form of HTML-based interface.



* Cloud: n. An idiotic buzzword used to describe pretty much any website these days.