Bootmanager disappeared? idk

[scarlet geyser]

I have Linux Mint on one drive and Windows on another and could choose which to boot, from the bootloader on the Mint drive.

I wanted to reinstall Windows and ran into a problem that made me follow some random post.
I used CMD through the Windows installation USB to clean the Windows drive with diskpart and "convert gpt".

Now, this bootmanager is gone and the Mint drive isn't seen as a bootable drive anymore.
Sorry if this is too easy but I don't understand what I did and don't know how to fix it.

[leaden gull]

I am a beginner too but it is simple, it can be solved if you just found the way to access it by your computer's keys like esc key f1 f2 f3 f4 f5 f6 etc
what you should do is try all of those keys when your pc is just freshly opening, which means if you get over a short time limit, you got to restart.
(my laptop's key to get to access is f9)
try em all(at once or try to look on google/duckduckgo which key your pc has) and you may get a boot manager that you may or may not be used to, this is my boot manager when i use f9

just search on google to verify what i say since i just recently got my linux ubuntu, i used universal usb installer if that's of any clue for you.

i don't know about why the mint drive isn't seen anymore though, this is all i can help

[scarlet geyser]

I tried doing that but for me this list is empty, all files are still on the drive but it doesn't get recognized as bootable after what I did. Still, thank you for your detailed reply, I didn't expect that

[leaden gull]

There is under system file directory in that, you can look for bootmgfw for windows and bootx64 for linux. That’s all im gonna help with if it’s helpful. (EFI/bootx64 and windows/microsoft/bootmgfw)