Hey tantis14, If HCX is still stretching your network (ie you retained your IP address and Default Gateway), all of your VM traffic is being routed through your on-prem environment. This means that once it hits on-prem, it's unable to route back to AWS. At this point, You'd need to unstretch the network or move your VM to a new subnet that is not stretched.
Native VMC segments have access to AWS Linked VPC via the xVPC network.
There is no need of a VPN to achieve that.
However, when you stretch a network from On-prem to Cloud, using HCX or NSX L2VPN client, the gateway IP remains at On-prem.
So for any VM on this stretched network to talk to anything outside its own network, the traffic will flow back to On-Premises and in order to reach an AWS VPC, you would need to create a VPN or DX link. This routing needs to be configured at your On-Premises