Unfortunately this is a case of https://www.hyrumslaw.com/. jQuery was an implementation detail that some shared deck authors started to rely on. We’re now forced to either provide it indefinitely (despite Anki not using it), or encourage people to move to more modern approaches (a lot of what jQuery offered is available out of the box in browsers these days).
The breakage on AnkiWeb was unintentional, but now that it’s happened, I’m wondering whether it might be a way to nudge people to update their templates, without breaking things for the whole ecosystem at once. For cases where a shared deck author is no longer responsive, it may be sufficient to drop something like the following into the top of your card template.
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.4/jquery.min.js"></script>