A/T P tires in front, Highway LT's in back, any problem?

It’s not a problem at all unless any of the tires aren’t suited for the load or it’s going to be in awd or 4wd with different diameters.
ABS won’t even be an issue in my experience although grossly different diameters may be.
We put 1 or 2 new tires on our work trucks all the time. Some of them run around with the spare on 1 wheel almost perpetually it seems. And not likely same tread and likely not the exact same diameter (diff tread/brand/wear).

Y’all make mountains out of mole hills here…