These are called ladder jacks. They are available at most hardware stores that sell ladders here. In my region you’re still allowed to use them if you set up guardrails or are tied off. I was working on my own house in this video so there are no governing safety regulations for working in your own home. They are definitely VERY handy for small jobs like this where setting up pump jacks aren’t really worth it and where you can’t access the location via a man lift. With anything, there are risks -

This is a homemade ladder jack. It makes working from a ladder much easier & safer. It's designed to fit anywhere on a ladder and gives you a platform to stand on / use as scaffolding #diyprojects #ladderjack #ladderdrills #tooltip #toolsofthetrade #bluecollartips #carpentrytools #carpentrywork #framinglife #sidinginstallation #masonrywork | Meyers.makes