After the roadmap is finalized, as the manager I ask every one on my team to stack rank at least N preferred projects from the roadmap. I map preferences to projects with some optimizations (e.g. career progression, avoiding knowledge silos), review it with everyone, and then commit for the roadmap.

If there's grunt work that no one wants to do, I distribute it fairly among the team. Fairly can be splitting it up evenly among the team (everyone refactors _n_ files) and sometimes it means we round-robin the responsibility (e.g. quarterly compliance reviews with auditors). Obviously this depends on the team size and role in the company, but I think it's only come up a few times over ~4 years.