Private NAT gateway can only be connected to one subnet. Let's say we have VPC1 and NAT-GW is connected here. We can connect to instances in VPC2 However when you want to connect from instances in VPC2 to VPC1, do you have to create a second NAT-GW in VPC2 ?
Yes, if the subnets have the same CIDR then you need to hide your subnet. You can create another NAT gateway for this purpose. It is also possible to use AWS PrivateLink or something else, but I focused here on NAT-GW.
you can use something else, but on the subnet where I created the load balancer you should have something that forwards the traffic, you cannot refer directly to the target network
This is a good post, but I'd recommend re-shooting the video. It is very fuzzy at the moment - one can't really make out what info you're adding into each screen.
Nat gateway is another point in the path that packets travel and can minimally extend it. If you are getting a timeout, it may be a configuration mistake. It's a good idea to use the Reachability Analyzer tool and see if there is a problem between the source and the destination.