A tax or VAT registration number in Settings → Regional is part of your studio records. It does not activate checkout tax calculation or register your business to collect tax.
Automatic checkout tax
Use Settings → You for your private business address and Settings → Sales tax for automatic tax guidance. Complete the connected Stripe Tax settings and the collection registrations appropriate to your business in Stripe. PayPal and Square checkout currently use that connected Stripe Tax service too.
The tax service uses the configured registrations and buyer address to calculate the checkout amount. There is no manual statewide rate to declare in Farbase.