And the biggie is that you cannot have private projects - which means that when you share a prototype with a client, that client also gains access to your design files and may copy those to their own Figma files.
Not something that you'd want in many commercial contexts, of course.
So if you are serious about Figma and creating prototypes/design files for use in commercial work, it is strongly suggested to avoid using the free tier.
But seriously: just create a free account, download the desktop app, and try it out for yourself. The limitations of the free version are clearly spelled out on the pricing page:
Compare plans across both Figma and FigJam. Explore features (including Dev Mode), pricing and frequently asked questions.
www.figma.com