It depends on vaccine effectiveness and your goal. For herd immunity, you’d want enough people with immunity through past infection or vaccination that the likelihood of someone passing on the infection to someone else is very low. I don’t know if that is achievable, with current vaccines and how effective they are against variants.
But as many people as possible would be my answer. Vaccines are just part of a multilevel approach that includes social distancing informed by hotspot monitoring, development or identification of medical interventions for people with infection, etc.
I have seen opinions that use of vaccines in people unlikely to have severe Covid outcomes will promote resistant strains but have not seen much evidence of this. Vaccine resistance involves different mechanisms than drug resistance, and can easily arise by chance with uncontrolled transmission in the population.
So vaccination of any and all that vaccines are authorized or approved for, if the goal is to minimize transmission and adverse outcomes while keeping a risk-averse government and population comfortable with staying open for business.