A simple way to think about this problem is simply in terms of which planetary orbits are stable in a given binary star system.
Let's talk about S-type orbits, where a planet's orbit around its star is smaller than the mutual orbit of the two stars. There is an outer edge of stability: planet orbits that are wider than a certain distance are unstable. That distance is directly linked to the closest approach between the two stars, Rmin. The ballpark number is generally 1/3: orbits start to be stable at about 1/3 of Rmin. So, if the two stars' closest approach is 30 AU, planetary orbits are stable out to about 10 AU. This is not a really firm number, because it depends to some degree on things like the stars' masses, how eccentric the stars' orbit is, and how inclined the stars' orbit is relative to the plane of the planets. But it's a good ballpark number.
So, for your case of a binary separated by 20 AU, you could plausibly have planets orbiting both stars out to, say, 6-7 AU. 788
If you want to be conservative put the edge at 5 AU. If the stars have different masses, then the more massive star can have planets farther out. If the binary orbit is eccentric, say with e=0.5, then the closest approach distance would be 20 AU * (1 - e) = 10 AU, so the outer edge for stable orbits would be at around 3 AU.
Of course, you can pack as many planets as you want interior to that radius (see here for example: https://planetplanet.net/2014/05/21/building-the-ultimate-solar-system-part-3-choosing-the-planets-orbits/).
You could also have planets orbiting exterior to the two stars, on P-type orbits. The ballpark criterion for planets on P-type orbits is that the inner edge of stability is at least 2 times the maximum separation of the two stars. So, for the case of your binary separated by 20 AU, you could have planets orbiting past ~40 AU (or, to be conservative, past ~50 AU). If your binary has an eccentricity of 0.5, then the farthest separation of the two stars would be 20 AU * (1 + e) = 30 AU, so you could have planets anywhere past 60-ish AU. Again, there are lots of details but this is the simple ballpark way to think about it.
And FYI see here for a summary of the effect of binary stars on planets: https://planetplanet.net/2013/06/06/binary-stars-friends-or-foes/
This figure shows the punchline:
Hope this helps!
ps - HDE 226868: very nice detailed answer related to formation. 788