I don't know if it can be fully solved. It can be mitigated to some extent, but I don't know that it's a fully solvable problem.
Monero, for example, uses proof of work for the security and dynamic block sizes for the scalability, but eventually that could do some small damage to decentralization, although hopefully it should not be much since storage is decently cheap
Scaling block size is not a long-term scalability solution. Bitcoin Cash forked from Bitcoin to double the block size. Then they doubled it again. They continued this and it's now 16x Bitcoin's block size and there are calls to double it again because "fees are too high". Increased block size=increased resources to run a node. It's why most of Ethereum's nodes are hosted in one of three corporate datacenters. Very dangerous for decentralization.
All of humanity's transactions shouldn't be stored on the ledger, permanently, forever. That is a waste of resources and totally madness. L2s are the solution, they use the main chain for security but store transaction data off-chain. They also inherently increase privacy. Bitcoin has lightning and (soon) Ark. Lightning is secure, mature technology and it works without sacrificing decentralization. In the last two months alone, it has been used by Nostr users (decentralized twitter clone similar to mastodon) to send over three million tips in the last two months. None of those tips were on the Bitcoin ledger because none of them need to be.
Lightning doesn't absolutely require centralization, but it does cause it. Who's lightning nodes have the most liquidity? That would be places like corporations, BlackRock, etc.