Yes.

@Daniil Unplug it. Reboot and get to the same screen. The one that's missing is the one that it was.

@Daniil If you're wanting to see which one disappears, then you don't plug it in. If you are wanting to boot from it, then it should be plugged in basically from the time you turn the machine on. It will work if plugged in at points after that, but when the latest point is will depend on your BIOS, so the only assured answer to that is that it should be plugged in when you turn the machine on.

If you know which device it's displayed as, then you can experiment as to when you can plug it it. It could be the list is dynamic and you could plug it in while viewing the list. OTOH, it may not be.

@Daniil Did you previously have it plugged in from the time you turned the machine on?

@Daniil Then your system may not be recognizing that it is bootable, or the device in general. That may be a problem with your machine, the USB device, a USB hub you are plugging the device into, your BIOS, the BIOS settings, or how you created the USB device (the last is probably the most likely). The most likely thing to do is determine if you created the USB device/image in a way that the machine will recognize is bootable, given its current settings.

@Daniil You're going to need to decide if you want to use UEFI booting on your machine, or not. There will be a BIOS setting for it, which probably will list something like "legacy" as the alternative. Your USB device will need to be formatted/created explicitly for one or the other. In particular, if you are using UFEI, which appears to be your current setting and is the default for newer machines, then whatever process you used to create the USB should explicitly state that it works for UFEI.

@Daniil Potentially. I'm not familiar with that tool. In general, if you're creating a USB boot device, then you'll probably want to format it, unless there's stuff on the USB which you're wanting to keep. The image you use may, or may not, need to be compatible with UEFI/legacy.

Basically, I'd suggest looking for questions on Ask Ubuntu about creating a bootable install USB device. Someone's going to be able to go into more detail in an answer than I am going to be able to here in chat.

@Daniil It's nearly certain there are a variety of existing questions which already cover installing Ubuntu and/or creating bootable install media on a USB device. You'd probably be better off searching a bit first.

\o/

Well, I'd figure out which device /dev/sdb is and what is mounted prior to making a decision. Personally, I'd open a terminal and investigate, but there might be a GUI method of doing so. However, I'm much more familiar with the linux/unix command line than the various GUI programs that are available in different windowing systems/OS releases. I'd probably start with just a mount command and/or df.

@Daniil It takes time to learn anything.

@Daniil Based on that, it looks like /dev/sdb is the device containing your boot image/install media, so, no, you don't want to unmount it.

@Daniil Possibly yes to both, but given that it's going overwrite whatever is already there, I'd make doubly sure that's where you want to have your Ubuntu system. Have you already installed Windows? If so, then the answer is probably no.

I'd definitely at least do a fdisk -l /dev/sda prior to making a choice. You may need that to be sudo fdisk -l /dev/sda

@Daniil Yeah, that would probably not be good. :;

@Daniil Somewhere you're going to need space for your Ubuntu system partition (and potentially other partitions too). If you have a single drive on this machine, then that's likely going to need to be /dev/sda, but you will need to take care in how you are allocating space so that you are not overwriting what's already there.

If you just went with the defaults when installing Windows, then it's quite likely that Windows consumed the entirety of /dev/sda when it created a partition for itself. If so, you'll need to use some software which allows you to shrink that partition in order to have space on the device for your Ubuntu partition. If it's a fresh install of Windows which you don't mind overwriting, it may be easier to start from scratch with a plan for the partitions.

The output from fdisk -l /dev/sda should have had more detail, which should show if there is more unallocated space on the device.

When setting up dual booting, I usually don't just trust that the tools will get the partitioning correct, so do it manually, but they probably do a reasonable job at this point.

@Daniil OK. That's a good sign that this may be on the easier end of the spectrum, but "somewhere" doesn't really narrow it down enough to be sure of what's going on.

@Daniil You appear to have two disks. Your first one appears to be completely allocated to Windows. Your second one could have almost anything on it, but I'd guess that it was a removable drive of some sort. Are you intending to install your additional OS on the second drive?

Maybe not. It might have the capability to install within an image file on your original Windows partition.

@Daniil I assume you mean that you have 200GB+ of free space within your Windows partition. That's different than having 200GB of unallocated space on the drive.

@Daniil OK. I'd be interested to hear what happens.

o/

:54578443 That may indicate you should try rebooting without your USB device installed, but implies larger problems, unless it failed in shutting down prior to the reboot.

@Daniil That looks like what's needed at this point. It probably won't make things worse.

@Daniil I'd boot your USB drive and see what happened to the partitions.

@Daniil The one with Linux. I would have assumed the (previously unmentioned) backups aren't bootable.

When you were installing Ubuntu, did it mention that it was resizing a partition?

@Daniil If the Windows logical drive (i.e. the Windows partition) has not been corrupted, now you need to tell Grub to add the primary Windows partition to the list which it offers as an option to boot into.

@Daniil There was plenty of free space on the partition which was resized, so it's possible everything is fine.

@Daniil Looks that way.

@Daniil Looks like it should work.

@Daniil If it doesn't work, then the other answers on that question have promise.