https://wccftech.com/how-to/how-to-fix-windows-11-beta-channel-missing-wip-settings/

Microsoft recently made Windows 11 available to Insiders in the Beta Channel. Since this channel offers more stability than the highly active Dev Channel, many Windows enthusiasts wanted to move to Beta Channel to get the goodness of Windows 11 with some stability. However, several users reported being unable to do that.

Some Insiders experienced that there was no option available to switch between the channels in Settings > Windows Update > Windows Insider Program. If you have been experiencing this bug and can't see an option to switch to Beta Channel Insider builds, you can follow the steps in this guide to address the problem.