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!)

For anyone who felt "this is more about what routing than BGP" the next article linked at the end starts to really dive into the BGP parts and can be started directly from if you're familiar with any form of routing: https://quantum5.ca/2023/07/19/diving-into-autonomous-system...