Advice on Free Screen recorder software

Hi – first post and after some advice about Screen Recording software.

I have a presentation to create and I know I can do this in PowerPoint but I was wondering if anyone can recommend any free screen recorder software. I have a windows laptop I’d be using.

I’ve previously used Camtasia but don’t want to fork out for software.

I simply need to record myself talking through a presentation – presentation is around 20 mins or so long – i want to be able to download the recording as a MP4 or similar

any advice gratefully received