Noob question : How is that effective if "SNI travels on the network in cleartext"

SNI is part of the HTTPS request, which would travel through the encrypted VPN channel. All network traffic would travel through your VPN, which is encrypted. The other end of the VPN channel is in another country which doesn’t block the website.

Your computer <—-encrypted channel to VPN in other country—-> https communication to blocked website

What a country could do but we haven’t seen before, is block all VPN protocol traffic, effectively banning VPNs. This would be disruptive to business or politicians using VPN for privacy, so it’s not as politically feasible.

That's cleartext within your TCP/IP connection. If you use a VPN, that connection itself is encrypted.