I see now. In the article, if you click the Android tab, there are instructions for Sheets. But you're right, on iOS they don't mention Sheets.
Thinking now about workarounds, if you placed the URL in another cell, you leave a Hyperlink formula in your target cell, something that looks to the URL holder cell to complete itself. Something like:
=IF( D2 = "", , Hyperlink( D2, "Click Me") )
Needs testing!
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You can use the =HYPERLINK(...) formula. Start typing out that formula in the cell, and you will see the formula auto populate on the left bottom corner, click on the hyperlink formula, then type the link and label text in the correct format. For example: