This is almost certainly an artifact of the different vaccination rates among different age groups and the fact that infections among the young will generally not result in serious cases, regardless of whether or not they were vaccinated. The data is from Scotland, where the vaccination rates among those over 60 are over 95% while the vaccination rate for 18 to 29 year olds is about 44%, that for 30 to 39 year olds about 55% (and those for older middle age between 72% and 83%). Guess which age groups have always had more serious outcomes all through the pandemic...
Give me a study with rates of serious outcomes worse among the vaccinated after controlling for age and comorbidities and I'll take notice. Otherwise this is just statistical illiteracy being used for anti-vaxx propaganda purposes.