Are you beginner in WordPress theme development? Needs to know How to start step by step WordPress theme development tutorial.
Before you start theme development you need a basic knowledge of HTML CSS Javascript and basic of PHP.
WordPress 101 Tutorial YouTube channel list will defiantly help you to build and WordPress theme from scratch.
You can also prefer WordPress Theme Handbook that available wordpress.org.
Let me share you a list of youtube channel that are very useful to learn WordPress theme development.