"Clear All" button will not solve the "run in background" of apps or solve the issues with battery consumption. In some cases, it even can lead to more battery consumption due to repeatedly loading the killed app(s). This is not how Android memory management works.
Also, GrapheneOS is a privacy and security focused mobile OS, not intended to be a feature-rich OS like LineageOS.
Please note, I'm a GrapheneOS end-user and not speaking on behalf of the dev. team.