I've found that Pocket's bookmarklet is not reliable in Safari and Safari Technology Preview due to browser security measures against 3rd party cookies. This results in their official bookmarklet asking me to "Please login" every time I try to use it.
Fortunately, there is an easy work-around with a very simple bookmarklet:
window.location.href = 'https://getpocket.com/edit?url='+encodeURI(window.location.href)
You can use the Bookmarklet Maker to turn this code into an actual bookmarklet.