I have for many years used the app Focus to block sites that I tend to visit when my mind wanders… (ie procrastinate) 
However, Apple introduced the Focus function a while ago and I have really never given it a test, so yesterday I looked more into it. Is it correct that you can’t block specific sites with this function? I can block Safari, but I really need to visit some pages when I work, so for me the Focus function seems useless…
Or have I missed something!?
I use Flow to do the same. It doesn’t look like iOS/MacOS Focus offers that functionality. I’m hoping the third party Flow will be able to add functionality to trigger a focus status in the OS so I can get the best of both as neither on its own provides what I’m looking for.
It seems, that iOS is (currently?) not able to do so. There are changes coming to the Focus-Mode with the next iOS, but I have no overview, if something like this will be part of it.
And BTW, thank you for the two links, maybe there is a solution also for me to stop my procrastination… 
It seems to me that integration with Focus Modes would be a great bullet point in the feature list for an app like that. I would suggest reaching out to the developers of the app to see if they could add support for automatically enabling/disabling based on focus mode.
In the meantime, as a workaround, it occurs to me that when enabling a (system level) focus mode, a shortcut could be triggered which also enabled the app, or perhaps a specific profile within the app (if it supports multiple profiles). Conversely, when the focus mode is disabled, a shortcut could be triggered to disable the app (or app profile). In that way, the two could work together.
Of course, for this to work, you need two things: (1) the ability to trigger a shortcut when enabling/disabling a focus mode and (2) the ability to enable/disable your app from Shortcuts. I don’t know enough about the app to know if 2 is possible, and I believe 1 requires some hoops, but is doable (sorry, I’ve never needed such a trigger myself, I just recall reading about others doing it).
Apple implements website limiting as part of “App Limits” in your “Screen Time” setting.
Technically, this isn’t a block, but you can add a limit for a site and set it as “one minute per day”.
Since it supports having a group of sites sharing the same limit, you might set “Facebook, Twitter, Instagram” to one minutes per day, effectively blocking them, or “CNN, NY Times, Politico, Axios, and AccuWeather” to a total of 10 minutes. You can still override it by typing in your Screen Time PIN, but it’ll block you first.
Not quite what you’re looking for, but it’s the closest I know without paying for a 3rd party parental controls service.
The big problem, if you (have to) overrule it once, you will overrule it always!
It’s been a while since I last used it, but Freedom (https://www.freedom.to) used a local VPN trick to block sites on iOS.
Currently working on an app that does something like this, quite flexibly:
It’s going through a pretty big rewrite at the moment so I wouldn’t try installing it right now, but check back in a month and we’ll have the app for you 
Never thought about integrating with Focus mode but I’ll definitely see if I can add it in.
+1 for Freedom. Used it quite extensively whilst studying for the Bar Exam, and continue to use it to keep me from shopping during the day… blocks sites rather well, IMHO
Mind wandering can be a good thing or at least a sign that the task in hand needs rethinking or redefining perhaps by breaking it down into smaller parts.
If your mind is wandering it’s probably better to seek a reason rather than rely on yet another app. They do not provide solutions merely sticking plasters over an deeper problem.
Having been working at home for over 20 years I have come to rely on a non digital solution. It’s called discipline and no app will ever replace it.
I hear you, but it’s not that easy. My background is programming and there’s a lot of thinking, and sometimes waiting.
Two problems:
Yes, I have focus problems. Hence I want my Mac to help me focus in a better way.
I am happy for you that you don’t have these problems.
I have a licence for FocusMe, which is full of elaborate ways to control the inner wanderer…
It’s subscription and I bought the 3 year deal it on special offer a while ago (it was about £35, not it’s about £65)
It’s cross platform (Mac and Windows, not iOS as far as I know) and therefore not very Maccy, but it is really flexible and the developer is very responsive.
There’s a two week free trial and you don’t need to give your credit card first.
Which has reminded me, I got so distracted after reinstalling Monterey a couple of months ago that I forget to reinstall FocusMe. I must rectify that…
It’s not a bad thing it’s fine if you are waiting for something to happen take some time to play, just restrict yourself to a set time then get back to work. I am also a developer, when my brain says give it a rest I do just that, but I impose restrictions. As I said no app is ever going to be a solution as by their very definition you control them, not them you.