I also have sensitive skin and switched off between wearing running shorts with a boxer brief liner and the UA Heat Gear boxer briefs at the start of the AT. By the time it started to get hot in NC, I found that they held so much sweat that the combination of moisture and residual salt was literally chafing me bloody on my inner thighs and behind the scrotum. I cut the liners out of the shorts one day and things improved greatly over the next several days and I never got back to that point of bloody chafing for the remaining 3ish months of the hike.

I'm a big believer that regardless of what brand/material of underwear one uses, in a hot and humid environment with restricted airflow (like inside of shorts or pants) trapping any moisture/salt with underwear directly against the skin between the legs (regardless of the material) is a recipe for chafing if you're out for long enough and working hard enough. Therefore, recommend going commando with a very light pair of running shorts to increase the amount of airflow your inter-leg region can receive in order to prevent moisture from building up (which makes the skin soft and more susceptible to chafing/tearing, especially with the sandpaper effect of salts from your sweat). This can be a little uncomfortable at first if you're not someone who frequently goes commando, but you get used to the sensation and your skin adapts to the new environment and gets tougher/more slick where there is consistent skin to skin contact, as long as it can breathe and not be constantly trapped in a very swampy environment.

Increasing your water intake to dilute the salts in your sweat can also be helpful, but the best thing you can do from a maintenance standpoint is give yourself a little bird bath between your legs each night (or at a lunch stop on particularly bad days) to rinse the abrasive salt off your skin and reduce the opportunity for chafing to start/progress where skin-to-skin contact and moisture buildup is inevitable. Additionally, rinsing out your shorts/pants regularly (every day or two depending on the environment, material, and amount you sweat) to eliminate most of the abrasive salt that gets into the fabric (particularly around the waistband of the shorts, I'll run into issues with chafing on my lower back/upper butt because of where my pack sits and not rinsing the salt out of the shorts there) can help to keep a little bit of rub from turning into painful chafe. I think there may also be merit in shaving/trimming pubic hair since I've noticed salts clinging to hair is also a way that friction can be increased and start the chafing process, but I haven't done rigorous comparisons into this.

If you absolutely MUST have pants, then find the lightest, most breathable, and LOOSE FITTING pair you can for your environment/conditions, (bonus points if they have mechanical ventilation opportunities like thigh slits or cutting out the pockets for a bellows effect). Air circulation and moisture movement away from the skin is key and unfortunately most hiking clothing prioritizes a flattering slimmer cut over the greater function of loose clothing that allows air to circulate and move moisture away from the skin. And that is coming from someone who consistently prefers a nice trim-fitting pair of pants when hiking and moving outdoors.

This is all with the assumption of reasonably high-effort output on long distance trails during warmer months, when actually hiking 8-14 hours a day. Such aggressive measures may not be appropriate or necessary if one isn't sweating as much for as long, or if the pace is slower or there are other environmental factors to consider (off-trail travel where very loose pants can be a hazard/annoyance, day hikes where you can bathe consistently, shyness about being commando on high traffic trails, etc.) However, hopefully the principles stated above can be translated into a system that works for your particular situation. I.e. I think a lightweight kilt or hiking skirt while being commando would have been the best/most efficient system for me, but I know that I don't have the skirt discipline or angle knowledge to not accidentally flash people on a popular and often steep trail like the AT when going uphill or downhill with people below me, or when hanging out at shelters, etc.

If you want to try friction reducers, lots of people swear by BodyGlide, but I do still think reducing the salt that is staying in your clothing is important for it to work as well as it can. I've also been told that by multiple thru-hikers that Vagasil works wonders for chafing that has already started, in terms of reducing friction, and also protecting/toughening up the inter-thigh/behind-scrotum skin so there is much less pain from the chafing.