You can use VPN and other proxies to overcome restrictions to access a website, but when it comes to investment it is different, you could invest if the project is not asking for KYC and if it is a public sale but you cannot invest as a US citizen during private sale.
When requiring KYC verification, there is no way for participants to join from countries registered in the prohibition on private sale, except using data verification services for relatives from different countries or funding other people accounts that have been approved in the whitelist with an agreement on the profit sharing system but the risk is high if he steals tokens from private sale.