After 35 years, the high F remains a work in progress for me.
One thing which has helped is simple exercises which uses this note frequently. For example, the first 6 notes of the C scale, starting from the high C. Also a steady breath will help. I find concern about not hitting the note affects my air flow at precisely the wrong time.
Of course, it could always be an excuse to upgrade your instrument. The Moeck Rondo is a decent intermediate instrument, however a more expensive model will probably be easier to play. Assuming you can afford it of course.
I see you’re in NSW Australia. So am I. If an instrument upgrade is feasible, perhaps a call to Zana Clarke at Orpheus Music would be the go.. Details at the Orpheus Music site
Mostly alto, plays with Balmain Baroque