Currently it cost $0.000116736 USD (1 satoshi) fee to make a transaction on lightning.

This is incorrect; there is no set price for sending a LN transaction. Each node can define its own policy for forwarding a payment through the network (base fee rate, plus a small percentage of the amount forwarded), so the fee paid will depend on the payment route taken.

In some cases (eg you have a channel open directly with your counterparty) there will be no fee for the LN payment itself.

Anecdotally, I think the most fees I have paid for a LN transaction is still in the range of single digit satoshis.

Can we just increase the decimals and have sub-satoshi fees for lightning?

LN nodes already track sub-satoshi amounts, with a resolution of 1/1000th of a satoshi. Note that these sub-satoshi amounts cannot be reconciled onto the base chain in the event of a channel closing, but they are still tracked by LN nodes, and in aggregate many sub-satoshi amounts can add up to whole satoshi values (which could then be settled on-chain).

What are some other scaling solutions to lower the fees?

The current LN fees are entirely defined by the network’s nodes. So it is a free market, wherein nodes can charge a small amount for the use of their liquidity in forwarding payments. If you want, you can run a node with zero fees, but many users will likely want some compensation for their liquidity availability.