It's on a progressive rollout so if you're not in the US, UK, Germany, France or Canada and logged into a Mozilla account you won't see it. If you meet those requirements, you can try force enabling it through about:config and setting browser.ipProtection.enabled to true

The Firefox built-in VPN is offered in stages to users in the U.S., U.K., Germany and France, as mentioned in the Firefox 149 release notes. It is also offered to users in Canada, starting in Firefox version 150. It is not available to everyone, even if you are in one of these locales.

If the built-in VPN is available, you would see a VPN icon in the top-right corner of the toolbar, that opens a prompt to turn on the VPN. You would also need to sign in to a Mozilla account. For more infomation, see the Use built-in VPN in Firefox article.

If you wish, you can post your feedback about the Firefox built-in VPN to the Mozilla Connect thread.

Charming. Patience, Grasshopper; much patience. The free limited VPN is most certainly NOT available everywhere. That info is provided more than once in its description. It's experimental. On trial. Imagine, from a business point of view, what would happen if Mozilla offered a free VPN to everyone. Infinite demand. VPN resources have to be paid for, so any business would 'test the water' before expanding any new offering. Yes? So just wait.