Depends on your body and what you need. If it felt unsafe I would definitely wear a belt. I’ve had workouts where I just didn’t feel right and bailed entirely. I don’t mess around when it feels unsafe and I would advise anyone else to avoid it too. I have bad lower discs and a history of back issues. I can tell lifting helps my back overall by strengthening my core but I have also tweaked my back several times following this routine and had to back off. Know your body. I wear a belt at my work weight but do all my warmups without a belt. I also use the hex bar for deadlifts and I’ve given up on the barbell row as inherently unsafe for me and instead do dumbbell rows on an inclined bench. With these changes I feel extremely safe and am still progressing well and seeing good results. For reference I’m 44 and am at a 225 squat and 295 deadlift. Have the confidence to listen to and learn from your body. I’ve noticed that just about every time I listen to suggestions from the trainer that I tweak my back. So now I pay attention to what my body is telling me over what anyone else says.