It depends on which programs you want to combine. Some work well together, others do not.
The most common combination members ask about is running the pull-up guide or muscle-up program alongside a main strength program. This can work if the total weekly volume stays manageable and you are not doubling up on the same muscle groups in the same sessions. The pull-up guide is specifically designed to complement a main program rather than replace it.
What does not work is stacking two full strength programs on top of each other. Each program already has the volume calculated for optimal progress and recovery. Running two simultaneously means your body cannot recover from either one properly, and both stall as a result.
The mobility program is the easiest to combine with anything. It is low intensity and supports rather than competes with your strength training.
If you are thinking about combining two specific programs, post in the community with the details and we will tell you honestly whether it makes sense for your current level and schedule. The answer is almost always to focus on one main program and use secondary programs as targeted supplements rather than equals.