Load a TY page, e.g. https://thankyou.wikipedia.org/wiki/Thank_You/en in Firefox 140 (or later, probably)
Open the browser tools and check the network for a request to https://en.wikipedia.org/w/index.php?title=Special:HideBanners&category=fundraising&reason=donate
It should load and set a banner hide cookie with reason=donate. Instead it is shown in red and a warning appears in the console: A resource is blocked by OpaqueResponseBlocking, please check browser console for details.
This is what I can find about OpaqueResponseBlocking:
https://github.com/annevk/orb
We may just need to set access-control-allow-origin: * on Special:HideBanners