Bitcoin Layer 1 simply cannot support this. 1 transaction per month from each person in El Salvador would use 100% of Bitcoins transaction capacity for that month.

What solutions are being proposed/implemented by these countries to make it viable - without using any/many Layer 1 transactions?

Are they using Lightning?

Are Banks providing BTC accounts, and then settling transactions on L1 occasionally with each other?

Is it something else?

How are they using Bitcoin to buy a 5 cent cup of coffee, with near-0 fees?