I installed macOS Monteray on my Macbook Pro 15 2014 via OpenCore Legacy Patcher in the past month. Was not happy with the battery life, so returned back to Big Sur by just erasing my SSD and installing new OS from the flash drive.

I ignored the instruction "Uninstalling OpenCore" not intentionally. Now I need to install Windows 11 and Ubuntu for parallel boot with macOS Big Sur. After installing Windows via BOOTCAMP I can boot it from boot menu, but why there is an Open Core logo? It confused me a lot.

https://preview.redd.it/oqq87nhskywb1.jpg?width=2989&format=pjpg&auto=webp&s=c0b7665d5947a5e9e22a0214a5bd98929fd63e7e

Now I have messed EFI volume (or partition) on macbook and disappointment after two days trying to install Ubuntu. I have a suspicion that Opencore may be the reason.

https://preview.redd.it/tfh9dj2bnywb1.jpg?width=1280&format=pjpg&auto=webp&s=86ca2123bf7b6cbe8e334b4c48e5aa8b846c4df5

I have followed the the instruction "Uninstalling OpenCore" now: removed everything from the EFI folder (becasue I now do not have any second OS installed) and reset NVRAM. That not helped and I still see OpenCore in Boot menu.

HOW TO GET RID OF OPEN CORE IN BOOT MENU?