Check out these youtube tutorials about it:
https://www.youtube.com/watch?v=ri98D-oZJnw
https://www.youtube.com/watch?v=6zS0OavqbAc
https://www.wix.com/corvid/example/Frozen-Header
https://www.dkm.agency/internet-marketing-blog/create-an-on-scroll-animated-header-using-wix-code-step-by-step
https://www.youtube.com/watch?v=5oKGTRlaa0w