Is it possible to use WordPress(.com) to build custom html,css websites as a free plan user?

I just had enough of the tutorials that seemingly have different options available than mine.

Adding custom CSS requires you to have plugins BUT INSTALLING PLUGINS REQUIRE YOU TO UPGRADE TO BUSINESS PLAN regardless if the plugin is free or not.

I can add custom html but I can't CSS or apply and create my own styles and I haven't found a single youtube video that allows me to put CSS as a free plan user without plugins and a business plan.

TLDR: I want to use WP(.com) but I am unable to apply my own CSS. I want to use it without a business plan or plugins. I want to be able to use flexbox properties akin to using VSCode or Code editor etc.

And if WordPress(com) is free as they say it is, why force users to go to a business plan?