We published a list of the 2020/2021 wrap-around season of the PGA TOUR here: PGA TOUR Tournaments. The list contains the tournaments as known, when the schedule was released in the fall of 2020. Each tournament in the list, where we could find a volunteer page, contains a hyperlink directly to that volunteer page. Consult that specific site for more info, for registration, to see, what's included in the volunteer package, etc.
We are still waiting for the 2021 schedule for the PGA TOUR Champions to be published, but will update our site as soon as we get firm dates.