I don't need, for example, color correction or motion tracking, but need to be able to cut / splice video clips, replace and add audio, and add some simple text (with font control) and transitions. And hopefully not tax my CPU (and practically non-existent GPU) too much while working on it.
I've used DaVinci Resolve for personal projects and it's amazingly fully featured, but too much for a simple instructional video, but it really taxes my laptop CPU (and I don't want to get a gaming machine to run DaVinci more efficiently.)
On the other hand we have Windows' built-in video editor which is basically too simple to do anything productive in.
https://www.techsmith.com/video-editor.html
For something free, I've had success with OpenShot and used it for show & tells at work on a work machine that I didn't have a licence to use anything more 'professional' with but be prepared to finnick about with it, but for your simple use case it should do the trick. You can use OBS (https://obsproject.com/) or ShareX (https://getsharex.com/) as free tools to capture the screen and/or your webcam.
Screenflow these days look like the only simple and robust editor with all crucial screencasts features.
(Ive been paying customer of both for a while, as a tutorial screencasts producer/youtuber)