As far as I understand Bitcoin mining the block reward consists of newly emitted and transaction fees. However, this new emission will disappear in the future and there will be only be the transaction fees.
Therefore, mining will be profitable if Bitcoin has a certain amount of on-chain transactions.
My impression is that people in future will rather rely on off-chain transactions due to the long block times.
My question is: Could it be a long-term security risk for Bitcoin if there are too few on-chain transactions after the last Bitcoin was mined?