What if governments ban exchange apps?

Probably a dumb question, but I was asked this question and I didn’t have an answer.

Bitcoin is government agnostic. It’s decentralized and global. However, exchanges are centralized. I use cash app to buy and send bitcoin. (Notice I didn’t say sell. HODL baby)

If tomorrow, the government bans exchange applications, it’s true, I still have my coins on my cold wallet, however, how would I buy or, more importantly, send BTC? Can’t the government block specific URL’s to access exchanges from operating? I’m sure I’m oversimplifying somewhere