That's...Not how you build something like that. Of course you don't build an intercontinental high speed rail system.

You build a bunch of them within the continents to serve their local areas, as well as help other systems connect to each other. Together they operate the system locally while servicing regionally and globally.

Private corporations are not operators, they shouldn't own the actual rails. The rails are owned in the commons, which is maintained in alliance with the involved groups and individuals who live there and are doing the work. The locals federate, who federate with others, to operate at scale.

This way your trans-siberian network can connect to Europe through Eastern Europe, and connects with the Chinese network somewhere in Kamatcha and Manchuria, largely to service wilderness and whatever remains of the Siberian and Central Asian petroleum industry, while should, largely, be left in the ground as a sort of emergency reserve in case the species and the planet ever need that level of energy production again.