I created an issue in the vscodeR a while ago (https://github.com/REditorSupport/vscode-R/issues/611#event-7005534822), but it seems that this hasn't been included. One way I am using is to create a shortcut for option settings, so that you can resize the plot interactively in each chunk.

options(vsc.dev.args = list(width = 800, height = 800))

Since I often work with the rendered pdf via pandoc, the parameter settings at the code chunk (fig.with and fig.height) should still be fine.