Simple filterlists, by definition, only work for a short time. Maybe a specific userscript can help. There are also Extensions, which redirect to articles about the same content to sites without paywall, like Unpaywall do, which is maybe the best option.

In Firefox, to use userscripts, you need to install first an Userscript Manage, like Tampermonkey, Violentmonkey, etc. which you find in the Mozilla Store. In Vivaldi it isn’t needed, simply download the script to a folder (don’t delete it) and drag it to the Extension Page in Developer mode in the Browser, to install it directly as an extension.