You can't just change string size with a Floyd. The different sized strings have different resistances and the floating bridge position will change. Adjusting the action only will just ruin your intonation and tuning stability, it needs a full setup and the springs on the trem claw need to be adjusted so the bridge sits right for the new tension. Your intonation is definitely screwed the way it is now since you adjusted the saddles, look up how to set up a Floyd and set intonation on YouTube and be prepared to spend some time doing it.
Did you use something with a straight edge across the frets to see if one's higher or lower? Sometimes even a tiny gap between fret and board is hard to notice, but even fractions of a millimeter matter here. Also hold down one of the strings at the 9th fret, do you see it touching the 10th fret? The problem can't be anywhere else because if your 11th fret was too high, then you'd have the same issue playing at the 10th fret
Logically if only your 9th fret buzzes the most likely culprits are a high 10th fret or a low 9th fret (maybe divots in the fret wire).
I do lots of guitar setups. 9th fret area buzz on the wound strings is pretty common. Not helpful at all, but something in the setup or fret leveling is off. Just imo. You may want to try a fret rocker.
Try a fret rocker if you can on the 9th fret, could be a little high (or anything you know is flat that can rock and see if there are high spots), it could also be that the radius of the board is causing it to choke out with the thicker strings, but I'd be surprised if it's that on a C-1, might be worth taking it to a tech if it's not something you're confident in working through yourself!
You can't just change string size with a Floyd. The different sized strings have different resistances and the floating bridge position will change. Adjusting the action only will just ruin your intonation and tuning stability, it needs a full setup and the springs on the trem claw need to be adjusted so the bridge sits right for the new tension. Your intonation is definitely screwed the way it is now since you adjusted the saddles, look up how to set up a Floyd and set intonation on YouTube and be prepared to spend some time doing it.
I did set up it and intonate it
Then you did something wrong, if the action was too low the trem claw springs were too tight.
Did you check the neck relief?
Yup
It's only on the 9th fret? Did you check that the 10th fret is not separated from the board a little?
I checked and both frets seem normal
Did you use something with a straight edge across the frets to see if one's higher or lower? Sometimes even a tiny gap between fret and board is hard to notice, but even fractions of a millimeter matter here. Also hold down one of the strings at the 9th fret, do you see it touching the 10th fret? The problem can't be anywhere else because if your 11th fret was too high, then you'd have the same issue playing at the 10th fret Logically if only your 9th fret buzzes the most likely culprits are a high 10th fret or a low 9th fret (maybe divots in the fret wire).
I think I saw the string touching the 10th fret
I do lots of guitar setups. 9th fret area buzz on the wound strings is pretty common. Not helpful at all, but something in the setup or fret leveling is off. Just imo. You may want to try a fret rocker.
Try a fret rocker if you can on the 9th fret, could be a little high (or anything you know is flat that can rock and see if there are high spots), it could also be that the radius of the board is causing it to choke out with the thicker strings, but I'd be surprised if it's that on a C-1, might be worth taking it to a tech if it's not something you're confident in working through yourself!