PilotWeb.org wrote:

If ATC uses the term "Cleared for approach" and/or gave you a clearance
limit, using the term "Cleared" then yes, you were operating under IFR.
The actual term IFR isn't usually used on the radio much, (they rarely
say anything like "Cleared IFR...") If you were "cleared for approach"
then you violated the regulations for operating under IFR without the
appropriate rating and without currency.

That is not what triggers IFR.

In my hypothetical I am on top of stratus 15 miles east of Podunck
Airport (which has a TRACON). I call in, "Poduck Approach, Baron 1234C
is at 8,500, VFR, over ACMEE intersection. Requst an ILS approach to
Runway 26."

"Baron 34C, radar contact over ACMEE, fly heading 270 for vectors to the
Podunck 26 ILS. Descent to and maintain 6,000."

Then, there could follow several altitude and vector heading changes
while I am IMC.

Finally, once the controller satisfies the vector-to-final requirements
of 7110.65P, only then will he say "Cleared for approach."