Probably it's not because of how many tx, but the computation power, thus you can have blocks near empty but they are resource hungry and congest the network.*
*It's only based on my common sense, it's like token transfer needs more gas than moving ETH, so probably minting and moving NFTs also require more gas.
This is not true. Did you even look at recent blocks? Some blocks have about 10 normal transactions, while during bull run we had 10 times more, and the network handled all of it. Why do you have to reply if you have no idea what you're talking about?