This question has been asked (and answered) many times here. Several users are very well versed. I believe the best answer was given by u/DarthNetflix (who provides great answers on a number of things, though we have disagreed before). See it here https://www.reddit.com/r/AskHistorians/comments/dx61ur/if_europeans_introduced_devastating_diseases_to/?utm_source=share&utm_medium=ios_app&utm_name=iossmf

At that post you will see a couple links to other good posts, full of interesting info and very worth reading, but both focus on the high mortality in the New World and glance over what happened in Europe.

A brief summary of all of these is that disease from the New World did huge damage in the Old World. However, a more lethal “cocktail” of diseases came to the Americas than back to Europe largely accounting for the wide mortality rate discrepancies. Additionally, many of the deadly diseases in the New World were already present in the Old. There is also the impact of population transfers. More people came from Europe and Africa than moved the other way. Ie more carriers to the New World.

To find more info, just search disease in this sub.