Polyurethane bushing squeak

Exactly. Follow the instructions, make sure all the fits and clearances are correct, lubricate generously. Never had an issue when they’ve been installed and maintained properly.
I tell you what I used to grease the last ones I had and will use it again. I use it on all kinda stuff, actually. Permatex ceramic based brake grease. Has a temperature range of -40 to 3000 degreesF. The stuff just flat works and stays put.