You know the advice is all primitive and I think you know that too, but let's talk about it anyway. I often buy such paraphernalia at https://obsessharness.com/harness-panties/ and I can share my experience. Only use panties during strap-on sex. It is unlikely that in normal life you would want to wear underwear with a ring or pin, opening the buttocks or having slits in the crotch area. Put on panties and attach a strapon to them. If you feel more comfortable, you can attach it before you put the panties on.

You can go to the mirror and assess your appearance in this outfit. You may feel out of place and even a little silly at first, but that feeling will quickly pass when you start having sex.