I use a microwave to warm my girls bottles, I just make sure to give it a really good shake. Ive never had a problem with doing it that way.
Microplastics
I use the microwave, I need to add gaviscon anyway so just stir it to avoid hotspots.
We always did it with my first, EBF this time so haven’t done it but we literally did all his bottles in the microwave not for long and shake them up lots and then let the air bubbles go back down. It was always fine
Hot spots from uneven heating. I just place the bottle in a cup of hot water and swirl it every now and then