MacOS on Apple Silicon for an extremely long time (maybe it's solved now? 2 years later?) which caused incredibly glitchy, almost unusable cursor movement if you let your battery drain to 0%, then plugged it back in and woke it from hibernate.
Screen Time in macOS is unbelievably, ludicrously, fully broken. Nothing about it works almost at all. Metrics for children don't show up. Web filtering falls open after a few hours at random (presumably because the background services crash). The "site not allowed" page predates HTML5 and randomly doesn't work. You can't block built-in apps like Apple News, the best you can do is set a 1-minute time limit. Tons of IP Addresses and Apple phone-home addresses get blocked on the "allowed sites only" mode resulting in constant popups. I had to pay for Qustodio because it's just useless. Also, it has elementary bugs that are horrifying. For example, the pane where you add allowed websites doesn't remember websites you just added when you dismiss it - so if you open the pane again without a reboot, and add another site, it forgets the one you added last time you opened the pane.
However janky other things might be on macOS, Screen Time with "Allowed Sites Only" is by far the most broken thing on macOS, bar none. Try using it with your younger children and rage in frustration as it crashes-open silently and allows Private Browsing with no filtering after a few hours.