This is called a MEGA / AMG Fuse (both registered trade marks)
BROWN / TAN colour is 500A. Max rated load current of 338A @ 20degC (rating chart in info below)
If you turn the fuse over you may find more info on the underside if is is not a window fuse.
This fuse (if fitted as some 500X don't have it) is the Starter / Alternator feed.
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