One thing they learn is PoW has to end rewards and switch to a Transaction fee based economic model.
*Which causes all kinds of problems for miner profitability , due to the winner take all design in PoW.*
There's no written rule, Dogecoin has infinite supply. Unpopular opinion, but I believe Bitcoin could hard fork, and change supply rules IF there was consensus.
Dogecoin and Monero have tail emissions, i.e. after an initial period of decreasing rewards, at some time they switch to constant rewards.
Grin is the first example of a coin with a never changing reward, from launch and forever at 1 Grin per second.