I use caulk and a few coats after it stops shrinking when it dries. You could tape the floor, use a 1” putty knife vertical to follow the contours of the trim. I use backer rod, a foam strand of various widths available, stuff it sufficiently back far enough 1/4” and proceed to fill crevice, run the putty knife vertical, maybe t shirt type material to wipe off the overage on the trim. Was thinking after it shrank and couple of coats to full height exactoknife the tape off but if floor moves those cut marks may be visible. So I’ve had lot of practice and am accurate. Not sure of tricks. I’ve caulked 3/4” gaps before from horrible carpenters going from tile to gluedown plank just for the challenge, it’s not a flooring guys responsibility, the apartments after we just left when done with flooring.
Uh, thought about you today, where a transition shouldn’t be(pic) I’m not even applying effort to remove it, just protect it from walking on. Eyesores hurt my eyes!