Correct Ethernet Jack + Magnetics for 100Base-TX
I understand the basic difference between 100Base-T and 100Base-TX ...


Are you sure? Maybe between 10BASE-T (original Ethernet) and 100BASE-TX (Fast Ethernet)?  Or between 1000BASE-T (Gigabit Ethernet) and 100BASE-TX?

Both 10BASE-T and 100BASE-TX work over two twisted pairs at once. While 1000BASE-T works over four pairs at once.

Making it shorter, people often write simply but mistakenly 10/100BASE-TX or 10/100BASE-T instead of proper 10BASE-T/100BASE-TX or 10BASE-Te/100BASE-TX to indicate that a MagJack support both (original and Fast) protocols.

Therefore:


On the Digikey page you referred to, there is no difference between selects in the Application field, select both and choose between all the will-be-shown possibilities;
On the Mouser page, there is no "simple" way to filter out only Fast ones.