To add to my confusion, I thought the 2020 4Runner was the 6th gen, I am seeing that it is still a 5th gen and 6th is not out yet even though these forums have a 6th gen section (remember I do not own a 4Runner), but it does appear that the cover I thought was identical to the IS was from a 2020 4Runner. So it is possible that the 2020 4Runner will fit the IS fuse cover.
I am taking this information from post #5 here, that cover looks identical to an IS cover, top tab and all.
2020 fuse box diagrams?