Unable to boot into windows after installing Ubuntu

This broke because you cannot modify partitions after installing Windows. By modifying the partitions, the Windows bootloader no longer knows where to find the Windows system boot files since they have been relocated (either a different partition number, or the physical location on the drive has moved). In fact, even if you only had macOS & Windows installed, you would still need to use Bootcamp Assistant to make any changes to the Windows system.

It should be possible for you to configure GRUB to boot the proper .efi file from one of the Windows partitions. This is basically what the Windows bootloader is doing...pointing to the system boot .efi file on one of the Windows partitions. However, there are multiple .efi files located on the various Windows partitions. It has been years since I tried to boot Windows from a Linux boot disk using GRUB, so I don't recall the specific name of the file or its location. I also don't know how Windows is set up on a Mac with Bootcamp. I've only ever done this with a standard Windows PC & Windows installation. It was usually trial & error for me anyway since I only did this when attempting to fix friend's & family members laptops with Windows (either corrupt Windows or failing drive). You will be on your own to figure this part out and you will need to review how to use the GRUB command line to edit or configure a temporary boot entry, or you will need to figure out how to configure the GRUB menu through Linux. The former is quicker since you don't have to boot into Linux each time you want to make a change. It will take a lot of experimentation. Keep in mind I have successfully done this years ago with Win7, Win8, and very early versions of Win10 so I know it is possible....it was some trial & error to make it happen.

You could also try booting from a bootable rEFInd USB stick (or boot into macOS to install rEFInd). The default configuration of rEFInd will scan for bootable volumes and list them for you. However, I don't know what rEFInd searches for when looking for bootable Windows volumes. If it actually looks for .efi boot files on all Windows partitions, then it may work. However, if rEFInd only looks for bootloaders on the hidden EFI (aka ESP) partition, then you will end up with the same result as the GRUB bootloader. Maybe rEFInd will allow easier custom configurations to experiment than doing it through GRUB, but I haven't used rEFInd in years either and never with Windows.

One of the Windows boot .efi files may launch the Windows recovery or repair tools. If it does this, then you could try to use the automated boot repair option to fix the Windows boot issue. Again, I don't recall the name of the file which would do this. This file may no longer resist with more recent versions of Windows since I do know that Windows has changed a lot the last few years and no longer has a special startup key even on dedicated Windows PCs.

If you cannot figure it out, then you will need to start all over again, hopefully the second time you will be installing Linux into a VM or to an external drive.

FYI, The problems you are having here is just one reason why I never recommend using multiple partitions on any drive. The second reason is people almost always realize much later that one or more partitions doe not have enough room. It is a lot of work & a lot of risk when modifying partitions. For people that want to use Linux on a Mac, I highly recommend installing Linux into a Virtual Machine if the workload & your system allows it, otherwise install Linux to an external USB3 SSD so that you minimize the risk to macOS on the internal drive.