“What are the long term side effects of gallbladder removal?”

Diarrhea

First of all, don't forget that the gallbladder is an important part of your body and it collects bile produced by your liver and releases it to the small intestine only when needed. If the gallbladder removed bile will be infused into the intestine all the time straight from the liver. This is an unwanted situation.
Read more about the role of gallbladder here: https://www.philahomeopathy.com/biliary-dyskinesia/

Generally, there is no major long-term risk, though some patients may get chronic diarrhea. There is also a small increased risk of small intestinal cancer:

https://www.gastrojournal.org/article/S0016-5085(01)21690-4/fulltext#:~:text=Among%20patients%20with%20a%20cholecystectomy,small%20bowel%20cancer%20(carcinoids).