The explanation why this happens and the solution if you insist on L2TP/IPsec is here; further in the discussion there are some suggestions what else to use, but in my case, I use SSTP clients on the remote Mikrotiks to manage them remotely. Be aware that using SSTP without at least a server-side certificate is not secure.
Other than that, Starlink will let through any tunneling protocol (IPIP, GRE, …) if encapsulated into IPsec, but you have to do the encapsulation manually, using tunnel mode of IPsec SAs rather than transport one.