We've moved them to all Apple devices. Locked down everything (the account on the Mac is "standard" not Administrator level). Set up a G Suite account with restricted access (cannot install apps, cannot install extensions into Chrome). Use 1Password for passwords, 2FA for all accounts that allow it. Removed Flash early on, removed Java runtime. Turned off auto–update on the Mac and iPhone/iPad.
I initially tried parental controls on the Mac but found it was a nightmare for even their limited use of apps outside of Chrome.
Still after 10+ years of “training” this person to call me for any technical issues I get surprises like yesterday when they wanted to install an “ad blocker that keeps popping up in Chrome”, which was, of course, malware.
Probably will ditch the Mac and switch to a Chromebook later this year.