Everything that has an advantage also has a disadvantage. Before online gambling started becoming as popular as it is today, which many can link to the COVID-19 spread that restricted people from leaving their homes, physical casinos and betting shops had also been producing gambling addicts.
Anyone can get addicted to whichever means they use for gambling; if you don't have self-control, you will get addicted even if it costs you a whole day to go and gamble. Some people won't mind as much as it's going to satisfy their gambling urge.
Online gambling was already on the run before the COVID pandemic broke out. It might have boosted the online industry quite a bit, I agree, but the wave of online casinos was on the way for many years.
Whether it leads to more addiction, I think there is a lot of research on the topic of availability and accessibility. If the hurdles to get something are very low and the effort someone has to put in to pursue a habit that impacts them negatively, then I think chances are higher that a negative habit will be pursued eventually.
If you are a smoker and you are out of cigarettes and the next store was 15 miles away, maybe you'd think it's not worth going those 15 miles to get cigarettes or alcohol or any other drug. But if there is a store around the corner and it takes you 2 minutes to walk there, probability is much higher you'll do it. Online casinos are a few clicks away. I doubt that many people who gamble in online casinos a lot would ever gamble as much in physical casinos if no online options existed.