If it's me, I won't use "F" as nomenclature. If it's fighter jet we build (although arguable), why not use Indonesian nomenclature instead?
"P-..." for "petarung" or "pejuang" for example.
About F33, it's not official yet.
for reference
https://www.naval-technology.com/news/singapore-mindef-type218sg-submarines/
Singapore need to spend US$ 1.8 billions for 4 units Invincible class along with training and logistics package