If you want to really use BGP without operating a real part of the internet, go and sign up for DN42. It's a pretend Internet built using Wireguard VPNs as if they were physical links.
One difference from the real internet: since traffic volume is relatively small and no money is exchanged, there's not really a distinction between transit and peering - you could do peering-only if you wanted to, but mostly everyone provides transit to all their peers, making the network a completely unstructured mesh (other than the large number of stub ASes who never bothered to get more than one peer!)
