I use cold turkey to block sites on Mac, it's really good, it's quite powerful with lots of options, many different blocklists and you can have a lot of control

I use cold turkey to block sites on Mac, it's really good, it's quite powerful with lots of options, many different blocklists and you can have a lot of control over it, i.e block things at certain times, time limit sites, or have to perform an action to gain access (i.e type some words, restart etc)