I am rushed for time but there is some research on the connection between marijuana and harder drugs. It is not conclusive. Here is one.
https://www.verywellmind.com/marijuana-leads-to-later-drug-abuse-63520
It appears one major factor is the age at which the person gets started smoking pot. To say there is NO connection would be totally incorrect.
My best buddy in HS, who is now deceased, smoked pot and we drank a lot of beer together in our younger days. Later on he got into weed and speed. We would go to Husker games and we stayed at their house with him and his wife. Years later I get a call from her saying they were getting a divorce. What? Turns out he got into meth - before anyone even knew what the stuff was. It was so hard to find he went to Denver to get it. It was just a few years before he passed away, my wife and I met up with him and he told us all those years we were running around he was high on meth and selling in out of his house. So, purely anecdotal, but he went from weed to meth. The happy ending is he finally got his life straightened out and worked part time helping others beat additions at the time of his death.
Another guy I know through my brother was an exceptional athlete in HS. He started smoking in HS, he would be about 58 now. I see him every few years and the last time he said he quit smoking pot because even the good stuff from CO (he lived there for several years) couldn't do anything for him. He is a shell of a person. No memory, very slow thinking, moving and seems to have aged tremendously. Again, just anecdotal.
I can't count the HS kids who I had as freshmen who were smoking pretty regularly and by the time they were seniors (if they didn't quit or get kicked out) were just a mess. Slow talking, slow thinking, really didn't much. These kids, to my understanding, were very chronic smokers. It really hit home to me to see these kids change so much. There is tons of research that tells us that young brains and weed do not go well together.