[noxer]

Its a long solved problem. Just years after bitcoin went live bitcoin devs figured out that PoW just cant be the solution. FBA (Federated Byzantine Agreement) DLT ("blockchains") where the result or making "a better bitcoin". There is no need to burn energy to solve the double spending problem. All you need is a distributed way to agree on Tx order. Whoever tries a double spend just f**ed up themself and simply wont know which one will be ordered first and which one therefore will be invalid. Thats not a problem for any honest participant.

See xrpl.org if you wanna read more in dept about this. There are plenty other protects using BFA instead of PoW/PoS by now.