After many users giving greatly valuable input, we verified that the below-described behavior is a result of a bug.
Using Safari up to version 15.4 (17622.214.171.124.13) will crash the text selection feature for .pdf's viewed in the browser once in-text search by command+F was initiated or once a character was entered into the search box thereof.
The behavior does not appear to affect all the pages, in fact, it seems the first or the first and second page remain unaffected; however, pages thereafter will not allow character-level, and multi-word text selection. What it means is once you want to select text it will select the first word that you begin selecting then it won't allow continuous selection of additional words, or characters of words or specific letters within that word — other than on page 1 or 2. It will simply select the single word wherever you begin text selection.
The question, therefore, is until a bug fix comes out: Is there any, for e.g., Hammerspoon scripts that could tie a "restart-pdf-viewer-in-Safari" command to every even calling of the in-text search feature? For e.g., such a restart command to every even command + F pressed while in Safari would already be terrific.
Alternatively, another command could call such a command resulting in the restarting of the in-Safari .pdf viewer.
For a little while now (basically after upgrading to Mac Monterey from Big Sur) and/or when I upgraded my Safari (now at 15.4), my computer (MacBook Air M1, 8 GB, 512) refuses to select text while viewing .pdf documents in the browser.
It is still able to search within the document, and the highlighted word, of course, is selected, and may be copied from the text, but simply hovering over the pressed cursor to select text does nothing in any .pdf's only, and I view dozens of them a day. (No, it's not because they are locked.)
Once I download them, of course, they work just fine, and I can select text. But I don't always (or often even) want to download documents.
Is there a setting that messed this up after one or both of the above upgrades?