What's the difference between "research grant" and "fellowship" ? (what to choose for a postdoc?)
Not sure what country you are in, but the usual difference between fellowship and grant funding in the UK is eligibility.

A fellowship is for somebody who does not yet have an academic position (that is, they are not a lecturer with an ongoing job). The fellowship supports them to do research that they choose and usually has a strong element of mentorship and other development.

On the other hand, a grant is for someone who already has an academic position and will lead the research. The academic wins the grant and then hires postdocs to conduct the research. The postdocs hired do not get to choose their research topic.