This achievement is like that chill friend who says, "No worries, you do you!". Hollow Knight currently boasts a whopping 112% completion, and you can mix and match whatever fits into that 112% to hit the magical 100%.
For instance, you can completely skip the Colosseum last trial, who needs that stress? Instead, you can dive into the Grimm Troupe content. You don’t even have to finish it! You can get some of the charms added on that DLC or, just beat all the Dream Warriors in their cozy little tombs. Not feeling that either? No problem! Go on a boss-fighting spree with the Dream Bosses to snag more essence and awaken the Dream Nail, which gives you an extra 1%.
There are so many ways to tackle this that it feels like a buffet of options, and that’s what makes hunting for this achievement so much fun.
Oh, and by the way, I highly recommend the Save Completion Analyzer for Hollow Knight Online. It’s very safe and doesn't do anything else than reading your save file, and the first page lays out what counts towards that 112%. The other pages? Pure gold for side-content!