Multitalented gives you a Dedication feat not a skill. Are you asking if you can get the Dedication feat, which likely does give a skill, then train that skill by using your Skill Increase at level 9?
If so I believe the answer is yes. There is no particular order to leveling up that would stop you from doing so.
You can perform the steps in the leveling-up process in
whichever order you want. For example, if you wanted
to take the skill feat Intimidating Prowess as your skill
feat at 10th level, but your character’s Strength score
was only 14, you could first increase their Strength score
to 16 using the ability boosts gained at 10th level, and
then take Intimidating Prowess as a skill feat at the
same level.
All good.