Thank you for your quick reply.
update-grub has not changed anything.
Here are the results of the other two commands you gave me:
lsblk
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NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sda 8:0 0 223.6G 0 disk
├─sda1 8:1 0 300M 0 part /boot/efi
└─sda2 8:2 0 223.3G 0 part
└─luks-b59fb893-54f4-4752-a46b-ce169da1d012 254:0 0 223.3G 0 crypt /
zram0 253:0 0 10.9G 0 disk /run/zram0
zram1 253:1 0 7.8G 0 disk /run/zram1
nvme0n1 259:0 0 931.5G 0 disk
├─nvme0n1p1 259:1 0 16M 0 part
└─nvme0n1p2 259:2 0 931.5G 0 part
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sudo fdisk -l
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Disk /dev/sda: 223.57 GiB, 240057409536 bytes, 468862128 sectors
Disk model: INTEL SSDSC2BP24
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: D233485A-845A-4610-9566-256A8951BC93
Device Start End Sectors Size Type
/dev/sda1 4096 618495 614400 300M EFI System
/dev/sda2 618496 468857024 468238529 223.3G Linux filesystem
Disk /dev/nvme0n1: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: SHGP31-1000GM-2
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 65E92CEC-DEED-4432-B034-559227EE1727
Device Start End Sectors Size Type
/dev/nvme0n1p1 2048 34815 32768 16M Microsoft reserved
/dev/nvme0n1p2 34816 1953523711 1953488896 931.5G Microsoft basic data
Disk /dev/mapper/luks-b59fb893-54f4-4752-a46b-ce169da1d012: 223.27 GiB, 239736029696 bytes, 468234433 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/zram0: 10.87 GiB, 11670650880 bytes, 2849280 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk /dev/zram1: 7.76 GiB, 8336179200 bytes, 2035200 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
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