Multiple Windows on Startup Items - How to Remove
Remove Windows from Startup Manager

You at least need to remove the hybrid partitioning on disk1. I assuming this drive would be /dev/sda under Ubuntu. If not, then make the appropriate substitution. The command below can be entered in a Ubuntu terminal window to list the drives and partitions.

sudo lsblk -e7


You can use gdisk included with Ubuntu to remove the hybrid partitioning. This is a interactive command. The command and user input is given below.

sudo gdisk /dev/sda
x
n
w
y


How to change EFI Boot to Ubuntu (Optional)

I noticed you have a icon for Ubuntu, but are still using the default label.

Enter the following commands in a macOS Terminal application window.

sudo diskutil mount disk1s1
sudo bless --folder /Volumes/EFI/EFI/Boot --label Ubuntu
diskutil unmount disk1s1


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How to Restore Hybrid Partitioning to the Windows Drive.

I assuming this drive would be /dev/disk0 under macOS. If not, then make the appropriate substitution. The command below can be entered in a Terminal application window to list the drives and partitions.

diskutil list


You can use gdisk installed in macOS to partially convert disk0 from a GPT to MBR partition table. This is a interactive command. The command and user input is given below.

sudo gdisk /dev/disk0
r
h
1
n
07
y
n
w
y


Next, use the following commands to finish the conversion.

sudo fdisk -e /dev/disk0
s 2
0
q
y
diskutil unmountdisk disk0
gpt destroy /dev/disk0


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