I have not heard of an web version of Insiders before your question. But there may be.
.
That page is broken. Although it has a tab for Web (Insider), it just repeats the Windows instructions.
.
At the bottom of the page there is a "Was this information useful" button. Click on it and comment on the problem with the web tab. Hopefully they will fix the problem, either by removing the tab or entering the correct information. In theory, it could be as simple as making a one line fix to point to the correct text that already exists. Include your email address. if you are lucky they will let you know when the page is fixed, but don't hold your breath waiting. Just keep checking the page daily for the next couple of weeks.
.
Please let us know if (when?) the page is updated.
.
************ Bonus Reading ***************
Earlier today I read this article about new features in Excel Online
Hint: some of the features also appear in Word Online
Online 2021 03 10- Excellent Excel for Web improvements
https://office-watch.com/2021/excellent-excel-for-web-improvements/
Excel in a web browser has some new improvements, many of them are familiar Excel desktop features moved online but one is unique to the browser-based version.
.
. * All Sheets: Status bar > All sheets icon > show list of sheet names
. * Better Keyboard shortcuts: Help > Keyboard Shortcuts
. * Change Regional Settings: File > Options
. * Multiple range selection: <CTL><Click>
. * More Zooming options
. * Zoom on the View tab
. * Version History: File: File > Info > Previous Versions
.