I think that there can be some training involved in regularly using diapers.
It might be helpful to start with what you already are comfortable doing. So, maybe an idea here is to wear your diaper and when you finally have to go then sit or stand at the toilet, as if the diaper wasn’t on. In time, sit on/stand by the toilet for just a moment when you need to go and then gently (not hurriedly) move away from doing it on/by the toilet, and release while standing or squatting by the bathroom door while closing your eyes and imagining you’re still at the toilet. Try to mimic and imagine being at the toilet for awhile so you simply get very comfortable with the sensation. Work your way up to no longer needing to close your eyes and imagine, and, eventually, no longer needing to be in or near the bathroom.
Take it all step by step instead of pressuring yourself to try to do it all at once.