With the release of v2.0.0 I've gone ahead and changed the package name from strapi-plugin-redis to @strapi-community/plugin-redis and likewise v2.0.0 WILL ONLY support Strapi 5 going forward.
If you are using this plugin on Strapi 4 then you will need to use v 1.1.0. I may or may not publish changes to the v1.x.x on the old package but thankfully this plugin takes very little to maintain and I haven't needed to in quite a while.
Do not attempt to use v2.0.0 on Strapi 4, I didn't test it but there is a pretty good chance it will not work.
If you have any questions or concerns please let me know.