However, there's no guarantee that alone will be able to pick up the slack if network capacity and transaction demand don't improve relative to falling block rewards. And really, it's hard to make a solid prediction regarding Bitcoin's fee market this far down the road anyway. We are at least half a decade away until this is even really a concern, and the network might very well be different by then.
Changes to scalability, Layer 2 development, increased adoption, shifting transaction behavior or new technology are all factors which could impact fee markets.
Even today, I am hesitant to predict what Bitcoin will look like in 5 years, let alone 10 a bit too speculative for my taste. Instead, I suspect the best strategy is to observe adoption and development trends.
Layer 1 and Layer 2 are mutually interacting with each other. People only have need of using layer 2, side chains, if transaction fees on layer 1 are expensive. If transaction fees on layer 1 are cheap enough, there will be less need of using layer 2.
Bitcoin is higher quality than Ethereum but I think using Ethereum and ETH layer 2 projects as an example is good enough. Layer 2 projects on Ethereum were very hot some years ago but when ETH layer 1 became cheaper in transaction fees, hypes on Layer 2 disappeared and many layer 2 projects on that chain have faced with very bad future.
They raised $B funds, developed their projects but if layer 1 is too good and cheap enough, layer 2 projects will naturally fail in selection of users.