If you can manage it, try visiting /boot/efi/ using ncdu to see what is using space where. Windows is not installed here, so I don't know how much space it requires. Mine has memtest files in /boot/efi consuming 1.2MiB, 1.0MiB, 896.0KiB and 24.0KiB; plus I have a BOOT using 1.1MiB and opensuse using 152.0KiB on an ESP filesystem of 320M, with total used of 4.4M and 315M available, for total use of 2%.

# tree /boot/efi
/boot/efi
├── EFI
│   ├── BOOT
│   │   ├── BOOTX64.EFI
│   │   └── mt74x64.efi
│   └── opensuse
│       └── grubx64.efi
├── MemTest86-Report-20200216-223015.html
├── MemTest86.log
├── mt74x64.efi
└── mt83x64.efi

4 directories, 7 files

Sorry I don't know what ncdu is. I have accessed the target folder (/boot/efi) using the file manager (dolphin) and I see size 31.9MiB, and 64.1MiB free of 96.0MiB (33% used)

There is a Microsoft folder inside using 26.2MiB but surely OpenSuse would have formatted the entire disk during the install? I have no reason to keep any old files from Windows and I feel like OpenSuse should have wiped the entire SSD during the install process or prompted me either way.

Is the Microsoft folder leftover from an old Windows install? Is it safe to delete it?

# zypper info ncdu

Information for package ncdu:
-----------------------------
Repository     : OSS
Name           : ncdu
Version        : 1.20-1.1
Arch           : x86_64
Vendor         : openSUSE
Installed Size : 107.5 KiB
Installed      : No
Status         : not installed
Source package : ncdu-1.20-1.1.src
Upstream URL   : https://dev.yorhel.nl/ncdu/
Summary        : NCurses Disk Usage
Description    :
    ncdu (NCurses Disk Usage) is a curses-based version of
    the well-known 'du', and provides a fast way to see what
    directories are using your disk space.
#
NCurses means does not require working X to use it.

With few exceptions, the installer's partitioner doesn't "format" any HDD or SSD. It normally formats partitions, volumes, floppy disks, legacy removable media, or sometimes USB devices. If you wanted to keep using the existing ESP without keeping any part of Windows, you could have checked the box to format the partition. The installer's partitioner only "wipes" the entire SSD when your partitioner proposal selection includes eliminating existing partitions, not when reusing existing partitions. "Wiping" isn't normal, but instead, creating a new partition table that eliminates the definitions of existing partitions. Wiping is an optional process.

In that case, I just want to point out that this was not at all clear during the installation process; if it had been, I would remember. I highly recommend having someone review the installation process as this was not at all clear to me: someone who has used Linux previously (Redhat in 2008, Ubuntu in 2012), and I work with computers on the regular. Considering updates are a critical part of modern OS functionality & security, having them completely broken out of the box is not friendly at all to new Linux adoptees. I have been wanting to recommend OpenSuse Slowroll to new Windows converts over the likes of Ubuntu/Mint but this makes me hesitate to recommend it. If I, an experienced user had trouble with this, how much moreso will a regular user struggle?

There's still the issue of the partition not having enough space, is it safe for me to delete the Microsoft folder?

(In reply to Aenos Edney from comment #4)
> I highly recommend having someone review the installation process

A complete replacement of the current installer is well along in development. Current installer seems to be in maintenance-only mode.
 
> There's still the issue of the partition not having enough space, is it safe
> for me to delete the Microsoft folder?

If your computer no longer has Windows installed, it's less safe to keep it.

Thank you, that is somewhat reassuring. I'm running into a problem when trying to delete the Microsoft folder: "Cannot delete: You do not have permission to remove items from this folder."

As far as I understand, Slowroll is not an immutable OS, which means I should have the power to do anything I like, including break the OS. Why is it blocking me, and how can I bypass this (without using the terminal if possible)

Sorry I seem to have figured it out. I'll document my method here in case someone else runs into this issue & tries Googling it:

Go back one folder in the Dolphin file manager, right click the EFI folder -> Open folder with -> File Manager - Super User Mode