Question about how Sets work in nftables

Hello! I'm new to working with nftables. While mastering this tool, I
had a few questions. Can you help me figure them out? 1) How does the
gc-interval parameter work in Sets? And how is it related to timeout?
2) What is the dynamic flag for? The Add, Update, and Delete actions
in the rules work without it. 3) What are performance and memory
policies? Thank you so much for your answers!