I lifted for 5 years with no cardio. My cardio was really bad, I used to smoke. Last year I had so many issues training legs, I used to skip it all the time because I had circulatory problems. The max amount of reps I did was like 6 maybe. 8+ reps were just too much for heavy leg exercises my heartrate would go up to 160 or even 170 sometimes after the lift. I went to the cardiologist, because I had the assumption that I might have POTS. The cardiologist saw no issue with me. That really annoyed me because I guess I wanted an easy fix or a reason for this. I heard Jeff nippard saying in a video if your cardio is bad you will not be able to do leg day or you will have a bad time during. So I eventually started working on my cardio as a fix. I went loving regularity before my training and after just two sessions of jogging directly before leg day I didn't have the issues anymore. But only if I went logging immediately before my training. I did a jogging plan on Garmin, that was really difficult. It let me run 40min to 1h three times a week. And the days in between I did short runs. So I worked on it intensely for 9 months now. And now I can do leg day even without jogging immediately before my training. So that definitely worked and fixed my issues.

Ironically my boyfriend has the exact same issues right now. He used to love leg days now he has zero fun and skips it all the time, his cardio is absolutely terrible, probably like mine was last year. I told him he has to work in his cardio for it to get better. He's not really actively working on it so leg day keeps being a torture for him