Select All in iOS Safari
‘Select, Select All, Speak Sentence’ are the options shown when there is no current selection. In your screenshot, a selection has been made, so the options change to be contextual to your selection, namely ‘Copy, Look Up, Share…’.

You can only bring up the first set of options without a selection, therefore this is only possible in a text input or textarea. You can make the entire page editable, thereby being able to place the cursor within without a selection, by running the following JavaScript in a Shortcut:

document.body.contentEditable = "true";