Comment # 1 on bug 1227385 from Felix Miata

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