Do you need to play Hollow Knight before Silksong?
No — Silksong is a sequel, but it puts you in a new kingdom with a new protagonist and tells its own story. The one real cost of skipping the first game is that it's a harder game to start on cold.
Team Cherry calls it a sequel, but the story and the systems are built to stand on their own.
No. Silksong is a sequel to Hollow Knight — Team Cherry has called it that since the game was announced — but it hands you a new protagonist, Hornet, in a new kingdom, Pharloom, entirely separate from Hallownest. The plot doesn't lean on the first game's story, and you're not picking up an old thread.
Where the two sit on a timeline is the one point people genuinely disagree on. Silksong is confirmed to take place after the events of Hollow Knight, but the original game has multiple endings and Team Cherry has never named one of them canon, so exactly how much time has passed — and which ending it follows — is left open. Treat any precise timeline claim you read elsewhere as someone's guess, not a confirmed fact.
What you actually lose by skipping the first game is context, not plot. Hornet appeared in Hollow Knight as a supporting character, and Silksong doesn't pause to reintroduce her: who she is and why bugs across two kingdoms already know her name land better if you've already met her there. It's a gap in flavor, not comprehension.
Difficulty is the real reason to play the first game first
Silksong doesn't require Hollow Knight experience to follow the story, but it does reward it for survival: it's noticeably harder from its opening hours than the first game was, with tighter platforming and boss patterns that assume you already know the genre's grammar. Go in cold and expect the learning curve the original spent many hours building to arrive within your first couple of sessions.
Once you're past the early game, the boss list and crest guide are where to go next.