[Samsung Galaxy S10 Questions & Answers] jonathanfv:
Okay, so I'm posting this to confirm: the bootloader on SM-G9750 is absolutely unlockable. I just did it. Huge thanks to [MENTION=1328551]warking[/MENTION] for pointing out the need for the USB drivers. Here were the steps (before taking those steps, make sure to back everything up):

Go to Settings/About phone/Software information, and tap on build number until developer mode is activated

Go to Settings, scroll all the way down to Developer options, and toggle OEM unlocking. It will issue a warning telling you security features might not work. If you want to keep going, then unlock it anyway.

Still in developer mode, activate USB debugging.

On a Windows PC, install Samsung's Android USB driver for Windows. You can download it from this official link: https://developer.samsung.com/galaxy/others/android-usb-driver-for-windows

Next you have to reboot in download mode. In order to do that, shut your phone down and boot again holding volume down, Bixby and power keys. Make sure your phone is connected to your computer through USB. Here's a note: the first time I tried to boot to download mode, it didn't work, it just booted normally. I needed to fist boot to recovery and then use the option to reboot to bootloader in order to be able to directly boot to download mode afterwards. If that is your case, you boot to recovery by shutting down your phone and then powering it up holding power, Bixby and volume up keys. Alternatively, you can use USB debugging to make your phone reboot to recovery through the command "adb reboot recovery" from the SDK Platform Tools. Also note that for me, I only got to "proper" download mode from using the keys to power my phone up. It wouldn't go to proper download mode if I went from recovery or from adb command. And your phone has to be connected to your computer when you do it.

If you entered proper download mode, you will see a screen with a big "WARNING" about installing custom OSes. You have three options. Click volume up once to continue to regular download mode. Click and hold the volume up key to unlock your bootloader. And click volume down to cancel and restart. Obviously, you'll want to long press the volume up key.

Once you do that, and other screen pops up asking you if you really want to unlock the bootloader, saying that it will wipe your personal data. From what I read, it's not supposed to wipe out SD cards, but I didn't take a chance and pulled mine out before going through the process. If you're okay with that, press volume up. Your phone will reboot, and a black screen I failed to photograph will pop up saying that your system is insecure (or something like that) and needs to wipe your data. It says to press the power key to continue. If you don't press the key, it will reboot again anyway and wipe your data on its own, so you don't really have anything to do from there on. It's simply going to be like a factory reset.

If you go to Settings/Developer options, your OEM unlocking option should be greyed out, and underneath it should be written "Bootloader already unlocked".

That's it. Your Snapdragon S10 series phone now has an unlocked bootloader. It probably looks much the same as for the Exynos variant, but it goes to show that SM-G9750 (Hong Kong and Chinese) models can have their bootloaders unlocked. I do think that depending on the amount of development you need, SM-G97x0 are excellent models to get, and I hope that more people will get them and work on them.

Note: Some other sites say you need to toggle OEM unlocking in developer mode, then remove your Samsung account, then install CROM and use it to unlock your bootloader. This does not work. Don't waste your time with it. Also, certain sites report that Samsung has a security feature that makes it so that people have to wait one week before being able to unlock their bootloader after having toggled OEM unlocking. This was not my case, but it could be the case for others. I don't know at this point. But keep that in mind.