What scaling means
Scaling is not just transactions per second. Transaction size, settlement time, cost, privacy, availability and the resources required to verify the rules independently also matter. A system can increase raw throughput while making it harder for ordinary participants to operate validating nodes.
On the base layer, every full node attempts to verify the same valid history. Its space is therefore scarce. BIP 141 introduced block weight with a maximum of four million weight units, but that does not yield one fixed TPS number: transactions differ in size and can batch several payments.
Scarce block space creates a queue
When more data is waiting than near-term blocks can hold, users offer fees per unit of weight. Miners generally choose more profitable packages and a low-fee transaction waits longer. The capacity boundary creates a price for urgent settlement, but congestion can price out small payments.
Larger blocks would add near-term space. They would also increase bandwidth, storage and validation time and might make nodes or rapid block propagation harder to operate. There is no single physically ordained maximum; it is a coordination choice between capacity and accessible independent verification.
Higher layers do not remove the base layer
Lightning uses payment channels: participants lock funds on-chain, exchange signed state updates off-chain and can settle the final result in Bitcoin. Many updates therefore need no separate block entry. Payments can be fast and small, but require available liquidity and a working route through the network.
A channel must be opened, managed and sometimes force-closed on the base layer. A non-custodial user must protect channel state and monitor the chain or use an assisting service; a custodial wallet simplifies this by adding trust. Lightning expands payment capacity, not unlimited final on-chain settlement capacity.
Scaling is a stack of trade-offs
Output batching, SegWit, Taproot and efficient scripts reduce bytes or weight per economic action. Lightning, side systems and custodians may serve more transfers above one settlement, but they have distinct risks and trust models.
The accurate answer is therefore that Bitcoin can scale, but not by placing every daily purchase as a separate transaction in a global chain. The open question is whether the base layer and its extensions can serve many people without making access to self-custody too costly or complex.