Yes, screencasts are good, and IMHO people who struggle with instructions seem much better at re-watching the difficult part until they are able to do it than they are keen to re-read a section until they get it right.
However it is often essential to have an alternative form (eg transcription or at least summary of steps) simply because of discoverability - even with brief screencasts it can be awkward finding the content otherwise.
I see a lot of responses here automatically assuming that capturing institutional knowledge is about code, but there's so much more of business processes than code that needs to be captured, even in a tech rich environment.
I second videos. In fact, I'm trying to think of a way to make animations showing the interaction between microservices without hiring and animator. I'm leaning towards mashing our integration tests with something like Three.js.
If we find a better way to do something then we make a new video.
There's a team member who transcribes videos into google docs for people who like to read and search in google drive.
It's pretty simple and it works wonders for an international team.