You could use the cell properties from the table context menu (leftmost icon):
Regarding the PRs: #8163 got reverted in #8393, because the use case was not completely clear (see Table cell color in joplin 2.11.11?).
The only relevant PR is #10059. It handles the first row as header row, but at the cost that not all options are available at the table menu. I guess the question is: Are the cell properties at the table context menu sufficient or do we need them at the top menu, too? In the latter case, we would need to define the entries for the top menu manually.