My girl potty trained right before turning 2. She just straddles or balances on the big toilet. She uses a kids potty at home. I got her on the big pots right away and I think that helped with possible fear and aversion.
It took my daughter a while to warm up to public bathrooms, but once she realized it was either pee in public or hold it and be uncomfortable, she went and realized it wasn’t so bad. I got her this seat that I can fold up and put in my bag whenever we go anywhere. We tried it at home first so she could get used to it. It suctions to the seat so it doesn’t move around and has a bag so it doesn’t touch any of my stuff in my bag. https://a.co/d/8giY3D7
We take the kid potty with us. We set it up in the back of our van or SUV. Potty on top of puppy pee pad, bag with wipes, towels, extra diapers next to it. We typically have him sit when we arrive and leave places. If we are there a long time (like a playgroup) we bring him out to the car and go more. If we are staying longer than an hour somewhere and are too far from the car to return then we bring potty with us. We have had some success with a travel potty seat, but it's super awkward because you have to take off shoes and pants else the kids legs will be straight out in front. Too much prep work when he needs to go NOW in my opinion.