The short answer: Without more research, it's impossible to know for certain, but based on what we do know about the physiology of the pelvic floor muscles during orgasm and the principles of skeletal muscle strengthening, it’s not likely that orgasm is enough to strengthen the pelvic floor. That said, in general, sexual activity of all kinds is great for your pelvic floor, as it brings healthy blood flow to your nerves, muscles, and other tissues.
According to the American College of Sports Medicine (ACSM), when it comes to conditioning any muscle, you need a variety of exercises that include resistance, flexibility, and coordination. And, as research shows, truly effective pelvic floor strengthening routines require a decent amount of time and effort.
For example, to minimize incontinence, a general recommendation is for patients to aim for 10-45 minutes of pelvic floor muscle strengthening exercises, consistently completed 3 or more times a week, for 6-12 weeks. Orgasms, as fantastic as they are, don’t give your pelvic floor muscles an adequate workout. (On that note, neither do kegels.)
While there isn’t a substantial amount of research available on the physiology of the pelvic floor muscles during orgasm for those with vaginal anatomy, what we do know is that orgasm is usually associated with involuntary rhythmic contractions of the pelvic floor muscles around the vaginal opening — these contractions can sometimes be myotonic, as in your muscle contractions may become sustained and rigid during your orgasm — and sometimes people will also experience anal contractions as well.
The muscle contractions that occur are reflexive as a result of the process of the orgasm, and not specific strengthening exercises like your muscles generally require for fitness, especially if the contraction of your muscles is sustained in the orgasm.
You can actively contract your pelvic floor muscle for a potential boost in pleasure.
You can of course actively contract your pelvic floor muscle for a potential boost in pleasure during orgasm, but the actual time spent in climax is sadly not long enough to challenge your muscles to the point where they'll gain strength.