If you don't care about what system you perform the filesystem expansion, you can do it on the R4S.
If the filesystem for overlay/upper is f2fs then these instructions should work fine: https://github.com/anaelorlinski/OpenWrt-NanoPi-R2S-R4S-Builds/blob/main/docs/resize-f2fs.md
I adapted that info to work when the overlay fs is ext4, like from the OpenWrt image builder / firmware selector site: Resizing the hidden overlay filesystem when it is ext4 and not f2fs
Others have stated that the overlay fs gets setup on first boot so your method on a desktop computer might need to be done after doing a boot on the R4S.
Some of the steps in the linked instructions need time to finish before issuing the next command so don't copy/paste the whole list at once.