That is excellent that you have backed up your important user files & downloads. You are in decent shape should a clean install be necessary. And it could be a good thing to do even unnecessarily to clear off accumulated junk & manufacturer
bloatware. (You also have a 30 GB Lenovo partition that could get you back to factory state. It would remove accumulated junk but restore the bloatware.)
(1) I think that last picture you show is of Rufus that burned your ISO to USB media.
(a) Where did you get the ISO from? I hope it was from the official Microsoft site...
https://www.microsoft.com/en-us/software-download/windows10
Download Windows 10 - Currently, this is v.1803
Make a Windows 10 Installation USB drive or burn an ISO to DVD. As the site says, match it to the
Edition (Home, Pro, etc.), Language, & Architecture (x64/64-bit or x86/32-bit) of the computer on which it will be used. I don't know - but I doubt - there is something within the ISO itself that would restrict it to one or the other partition schemes (MBR or GPT). However, if you get it
from there, all doubt is removed. And you wouldn't need Rufus either.
(b) Where Rufus says, "MBR partition scheme for UEFI or BIOS" - it is speaking
I think of the partition scheme or style on the USB media - not the one on the HDD in the computer. The partition style on the USB drive will be MBR - that's fine. Also, sounds like it is set to make the USB media bootable whether BIOS is
in UEFI or in Legacy mode & whether the boot option chosen is for UEFI or Legacy. All is good with that, I think.
https://www.lifewire.com/how-to-burn-an-iso-file-to-a-usb-drive-2619270
How to Burn an ISO File to a USB Drive
Note: That's a 3rd-party site. Looks smart, but I know nothing of the links or downloads there.
(2) But the partition scheme on the HDD in the computer is GPT, going by the error message you got, namely "Windows cannot be installed to this disk. The selected disk is of the GPT style.". Therefore...
(a) You must set BIOS to be in UEFI mode.
(b) You must select to boot the USB drive in UEFI mode.
When the BIOS is in Legacy mode, it will offer just
one way to boot the USB media (on the BIOS Boot Menu screen) - Legacy mode. In that case, Windows must install to a HDD that is in the MBR format. Yours is in the GPT format. So, at that "Choose a partition" screen, you'd have to delete all the partitions, including the Lenovo partition & click "Next". Then Windows would reformat the HDD to MBR style automatically & create all new
partitions in which to install Windows. (You could do the same with BIOS in UEFI mode & selecting the Legacy boot option for the USB drive. But you will lose all the benefits of a UEFI install. It will be a Legacy install.)
However, if the BIOS is in UEFI mode, you may see
two ways to boot the USB drive. You must select the one that identifies itself to be
UEFI mode. Then, the existing GPT style is acceptable. And it will be as I wrote in my prior post. You could delete the top 4 partitions, select the unallocated space created, & click "Next". That's a true clean install, &
it preserves the Lenovo partition. You get all new Windows partitions, but no C:\Windows.old that would hold the current Windows version & files.
Or, you could select the 433.9 GB Primary partition (which is the current Windows partition), & click "Next". This is a clean install too, meaning no apps you've installed or that the computer manufacturer
installed will survive. Maybe it asks whether to keep files, I don't know. If not, those are gone too. However, you should get a C:\Windows.old that should hold everything including the files. The existing EFI system & recovery partitions will
be repurposed for the new Windows.
Here is a definitive write-up of a clean install...
https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install/clean-install-windows-10/1c426bdf-79b1-4d42-be93-17378d93e587
Clean Install Windows 10
See where he says, " (Note: If you did not rescue files stranded in C using the bootable media step earlier, you can save them here. Instead of deleting partitions, just click on C and choose Next without deleting or formatting. This will archive your files in C:\windows.old. But it is not as clean of an install.)".
(3) But see what Kyle62 found...
https://mspoweruser.com/avast-issues-a-fix-for-the-windows-10-april-2018-update-problem/
Avast issues a fix for the Windows 10 April 2018 Update problem
Note: Another 3rd-party site. Looks good, but I know nothing of links or downloads there.
It's an excellent write-up of what others have been posting in this thread to achieve a repair-install that keeps everything. Except...
At step 9, be sure to match Edition (Home, Pro, etc.) & Language as well as Architecture (x64/64-bit or x86/32-bit).