iPad OS on recent iPads has a dead simple "limit charge to 80%" option in system settings. MacOS should just have the same feature.
I also limit my iPhone's charge by using shortcut automations and a smart power plug. It just turns the plug off when charge exceeds 80% and on when it drops below 75%. Not ideal but I think still better for battery life than having it sit at 100%. (lmk if I'm wrong!)