2 GRUBS - specific EFI System Partition x non-specific, can I remove one Disk?

I have three disks on my computer. One HDD, two SSD's.

ON HDD - it's only free space now. In the past I had Ubuntu there.

On SSD1 - there is Windows + EFI System Partition (which -probably- is where GRUB is installed. In the past, used this partition to dual-boot the old Linux install on the HDD with the Windows one)

Now, I bought a new SSD and installed Ubuntu. Let's call it SSD2.

ON SSD2 - Ubuntu only (not specific EFI System Partition) + partition for windows files.

On the install, in the "Device for bootloader installation" option I've chosen:

"/dev/nvme0n1p4" > format: ext4 Same partition that I've installed the whole system, not a specific EFI System Partition.

So here I have two questions. 1- do I have two GRUB's installed? I mean, if I remove the SSD1, will I be able to boot into the Linux only using SSD2? 2- Is there any practical consequences to install the bootloader on the system partition (like i did on SSD2) instead of some specific EFI Partition (like I Did on SSD1)?

Did some research, and was still a bit confused, however, got some commands that can be useful to clarify my current situation to you:

sudo fdisk -l

Disk /dev/nvme0n1 (SSD2 - New): 232,91 GiB
Device             Start       End   Sectors   Size Type
/dev/nvme0n1p1        34     32767     32734    16M Microsoft reserved
/dev/nvme0n1p2     32768 253513727 253480960 120,9G Microsoft basic data
/dev/nvme0n1p4 254513152 488396799 233883648 111,5G Linux filesystem


Disk /dev/nvme1n1 (SSD1 - Old): 119,25 GiB
Device             Start       End   Sectors  Size Type
/dev/nvme1n1p1      2048 249659391 249657344  119G Microsoft basic data
/dev/nvme1n1p2 249659392 250068991    409600  200M EFI System

lsblk

sda (HDD)           8:0    0 931,5G  0 disk 
└─sda6        8:6    0   7,2G  0 part 
nvme0n1 (SS2 - New)     259:0    0 232,9G  0 disk 
├─nvme0n1p1 259:1    0    16M  0 part 
├─nvme0n1p2 259:2    0 120,9G  0 part 
└─nvme0n1p4 259:3    0 111,5G  0 part /
nvme1n1 (SSD1 - OLD)     259:4    0 119,2G  0 disk 
├─nvme1n1p1 259:5    0   119G  0 part 
└─nvme1n1p2 259:6    0   200M  0 part /boot/efi

sudo efibootmgr -v

BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0000,0002,2001,2002,2003
Boot0000* ubuntu    HD(2,GPT,giant_number)/File(\EFI\ubuntu\shimx64.efi)RC
Boot0002* Windows Boot Manager  HD(2,GPT,giant_number)/File(\EFI\Microsoft\Boot\bootmgfw.efi)WINDOWS.........x...B.C.D.O.B.J.E.C.T.= (giant_number)......
Boot2001* EFI USB Device    RC
Boot2002* EFI DVD/CDROM RC

Solution 1:

I can see only one instance of grub installed on your system and this instance is installed to your EFI System Partition /dev/nvme1n1p2 (SSD1 - OLD).

If you remove the drive which holds the EFI System Partition you will be unable to boot either OS on this machine.

Installing an instance of Grub to the OS-partition does only make sense in legacy-mode, but not in UEFI-mode. In UEFI-mode the installer will try to install Grub to an existing ESP (the installer searches itself for a valid ESP) and ignores the choice of bootloader location you made.