Hi Sara M.,
Well, it depends on your clients and their users. Technically, a website doesn't have to be accessible to work.
It start to be a topic when you want to optimize for SEO. Google consider a good UX is a website accessible to most users.
If your client want to go further and make a website accessible, there are standards: (WCAG 2.1 AA)
https://www.w3.org/WAI/standards-guidelines/wcag/
Here is a great webflow ressource to get started.
https://webflow.com/accessibility/checklist#start
From where I'm from (switzerland) there are no "legal" part, it's just a recommendation to make website accessible. I believe some institutions have accessibility requirements to meet but on my side, I never heard of any law. Sorry, can't help you here.
