Bootcamp Error: The startup disk cannot be partitioned or restored to a single partition
Here is the commands you need to enter in a Terminal application window.

sudo diskutil eraseVolume free none disk0s4
sudo diskutil eraseVolume free none disk0s3
sudo diskutil apfs resizeContainer disk0s2 0


These commands will have removed the Windows partitions and expanded the macOS partition to recover the free space. However, there may still be Windows boot files stored in the hidden EFI partition (disk0s1). If these files exist, then they can be removed by entering the commands given below.

sudo diskutil mount disk0s1
cd /Volumes/EFI/EFI
rm -r Boot
rm -r Microsoft
cd ~
diskutil unmount disk0s1