Bootcamp failure at partition creation, can't delete it, how to start over?

I know this is a bit late, but for anyone else who finds this thread, I have a command line solution if Bootcamp Assistant and Disk Utility are unable to remove the Windows partitions. This solution will only work with a drive layout like the OP @user1247 has listed in their original post with an APFS Container and one or two Windows partitions after the APFS Container.

You need to get the identifiers for each of the Windows partitions. Using the OP's information, this would be "disk0s3" and "disk0s4". You will also need the identifier for the APFS Container as well which is "disk0s2" here. To get the drive layout for the internal drive, you can use the following command in the Terminal app:

diskutil  list  internal

Now with the Identifiers for the Windows partitions, you will need to use the following command to delete the partitions and convert them into Unallocated "free space". It is best to use the previous command after each of the following ones in order to confirm the Identifiers for the partitions has not changed.

diskutil  eraseVolume  free  none  disk0s4

diskutil  eraseVolume  free  none  disk0s3

Now if you use the "diskutil list internal" command again, you should see that the two Windows partitions are gone and have been replaced with unallocated space listed as "(free space)".

You can now expand the APFS Container (disk0s2) into the unallocated (free space) area by using the following command (the last character is the number zero):

diskutil  ap  resizeContainer  disk0s2  0

Before attempting to modify any partitions on the drive, you should make sure you have a good current backup just in case something goes wrong and the macOS partition/Container is damaged or deleted. Modifying partitions and drive layouts is always a risky procedure even when using the Disk Utility GUI app. The Terminal command line has no safety nets and even a simple typographical error can have devastating & unintended results.

I have tested this on a similarly partition .dmg image file I created and these commands worked fine. Tested on macOS Ventura, but it should work on macOS 10.13 High Sierra up to the current macOS 14.x Sonoma where an APFS Container is being used. Older versions of macOS using the HFS+ (aka MacOS Extended) file system instead of the APFS file system will require different commands to achieve the same results.

If Bootcamp Assistant is unable to remove Windows, then you can try using Disk Utility to delete the two Windows partitions shown in your screenshots (disk0s3 & disk0s4). Make sure to delete "disk0s4" first, then "disk0s3". Unfortunately many times Disk Utility will not re-merge the space used back into the main macOS Container (aka partition) in this case "disk0s2". It may be possible to use the command line "diskutil" command to merge that space back into the "disk0s2" Container, but I don't have the time or a spare drive to experiment. I do know there is at least one thread on the Apple forums from a few years ago where I assisted another user with this issue, but the user had to modify my two suggestions before it actually worked. Unfortunately I don't recall the exact options to use with the command.

Otherwise you may find it quicker & easier to start completely over by performing a clean install of macOS by first erasing the whole physical SSD followed by reinstalling macOS & restoring from a backup. Then attempt to use Bootcamp Assistant to install Windows again.

No matter what you do, make sure you have a good backup of macOS now while you still can since modifying partitions is always a risky endeavor that could cause you to lose access to your data.