Reverse engineering is not against the law in the US or Australia. In the US, emulators and reverse engineering have a decent amount of legal protection, especially for archival purposes.

The case with Nintendo and Yuzu is a weird one because apparently those devs were kinda shitty, didn't release a lot of their source and charged for certain releases. There are other open source/free Switch emulators (that still require you to provide your own Nintendo BIOS/ROM dump, so no infringement in the code) that Nintendo hasn't touched.

This is also for reverse engineering multiplayer protocols for a game service that is literally going away forever. In the 90s, games allowed you to run local servers on your network using the game itself (like Counterstrike). Blizzard was the first to go after the opensource bnetd, which let people setup Warcraft/Starcraft servers locally instead of depending on Blizzard. They caved and went away, but they didn't actually test the case from a legal perspective.