Hollow Knight is the greatest game of all time for me. I replayed it recently and it was such a different experience for me to move through confidently and quickly when I had a grasp of combat from the beginning. It took me months to finish it the first time because of getting lost and not knowing where to go next.

Some generic (no spoiler) tips:

• go in another direction and come back to the boss later if that's possible. If a boss is way too difficult then there may be an upgrade you haven't gotten yet.
• take your time. It is more important to save your health rather than rushing to get a hit in. Sometimes it's worth going to a boss and not hitting him at all and just focus on learning movement, patterns and figuring out where the openings are.
• play around with your charms and get the best setup you need to help with the boss fight.
• try to avoid attacks by running into the gap in projectiles rather than relying on dashes all the time.
• if you're coming to thinking of quitting the game based on difficulty, then there's no shame in watching a boss guide video on YouTube. Or space it out with a secondary game so you can play something else and come back later.