I use IntelliJ IDEA and often rely on their own Git functionality. But it cannot stage specific lines, only whole chunks [1]. For that, I've been using lazygit for a couple of months now. I like its simple UI and that it makes staging specific lines very easy and quick. If you like lazygit, you might also be interested in similar Git CLI clients that I collected here [2]. [1] https://youtrack.jetbrains.com/issue/IDEA…
In Rider, there are features that allow committing individual lines instead of a whole file. You can select in the commit dialog which lines to include/omit. Also I recommended taking a look at Changelists feature that allows separating certain changes from what would be committed next (I believe it works line by line basis).