I need advice Bees!

LO is a little over 2.5 years. I can say we are 99% HOME potty trained (except for naps/sleep). I can confidently let him wear his underwear and 99% of the time he would let me know he needs to pee/poop. Even if he had an accident he would somehow be able to hold it and scream/cry so I can quickly swoosh him to the potty. He also started holding his pee when we were in the car too. Just over this weekend we were on a short road trip, he actually held his pee until he got home (Poor guy)! Today when we traveled from daycare to home he also held his pee until we got home.

The dilemma is, he WOULD NOT use any other potty outside of our house.

I've tried multiple times to take him to "tour" the bathrooms whenever we were at a restaurant. I asked if he would like to try and he said he wouldn't. He wouldn't even let me take his pants off. At school, he uses the potty for 1-2 times for the whole day, and the rest of the times he go in his training diapers . There are times he would sit on the potty and wouldn't pee whereas at home, he always pee whenever I put him on the potty.

I talked to my friend about this issue, and she said I could demonstrate on how to use the public potty, which I did for 3 times over the weekend, but he still wouldn't try.

We are still using training diapers when we go out or go to school. The school didn't give us green light to use underwear yet (because he hasn't been consistently using the potty) so we can't anyway. And I am very chicken about public accidents. My friend said maybe LO is not really ready yet.

We have a potty seat on top of the toilet at home and there is a pee-guard in front. So whenever he uses the potty, he is completely pant-less / shoeless and he can sit comfortably. This is not something that is doable at school or outside. I am guessing that's one of the (many) reasons why he refuses outside potties.

What do you think? Did anyone go through a phase like this and does it naturally go away? Or what did you do to help LO use the potty that is outside of his home? Or just any advice is welcomed.