I could really use some help/pointers "refreshing" my Windows install & dual-booting properly

Operating Systems & Open Source Windows
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Mobo: ASUS ROG STRIX X370-F GAMING
CPU: AMD Ryzen 7 5800X3D
RAM: 32GB Trident G-Skill (4 sticks)
GPU: RTX 4070

I could really use some advice here. I have had this particular Windows machine since 2017 (with some occasional hardware upgrades). Recently I tried installing Linux Mint on a separate boot drive, to try dual-booting. However, ever since I have tried the dual-boot setup, Windows has thrown up errors and problems every now and then, including: failing to boot, entering recovery, going back to normal, asking me to reinstall current version of windows to repair (and failing)… Every time I use Linux, Window’s clock gets screwed up the next boot. Just a lot of buggy nonsense. I think I should just redo the OS setup more or less “from-scratch”.

Upon powering up the machine, I want to have a screen prompt asking me what OS I want to use for the session. I have not been able to get this to work, and after some reading I suspect it may have something to do with 1) my boot mode(?), and 2) it seems easier to do if both OS’s are on the same drive (which is not how I have it set up currently).

Brief tangent: Why did I put them on separate drives? I’m fed up with the feeling that Microsoft digs its greedy fingers into my system. Separate disks felt like a more tangible wall, but this might just be an ignorant psychological safety blanket, I freely confess.

Windows 11: Installed on 1TB M.2 NVME along with some software.
Linux: Installed on a different 4TB M.2 NVME with everything associated with Linux self-contained on its drive.

-I would love to be able to fix this without starting from scratch on both OS’s, but if I must, so be it. I would prefer to keep the Linux install as-is, if I can(?)… Are there ways I can fix/refresh my current setup so the separate-drive dual-boot works?

-Should I try using one of the M.2 NVMEs for both systems? I’d prefer to “stay in my lane” at first and redo Windows first (as I’m more comfortable and familiar with its workflows) and then prepare Linux. Or, should I partition the bigger linux drive into two and do a fresh install of windows there, then wipe the drive its currently on? I’m not sure what the best course of action is.

What do I need to do to prepare for this overhaul? What’s my order of operations? What settings do I change first? What are some tripping hazards I might not expect? If I have various programs installed on other Windows drives, will they cease to function after a completely fresh install (missing registry records or something)?

Any pointers and feedback would be greatly appreciated. I would probably have far less of a confusing problem doing this on a brand-spanking-new system, but I kinda wanted to hold out until AM6…

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I have seen this on my friend’s system that used Bitlocker - even a Live boot of Ubuntu, without performing an install, would cause Bitlocker to become sus and demand a recovery key to unlock. Not sure if this was an issue specific to Ubuntu at the time, or how to deal with it, or if it was already fixed. If this is what happened to you, then I don’t have a good answer other than to disable Bitlocker, which is OK if you’re not concerned about someone stealing your PC or SSD and access the data on it…

This is caused by Windows expecting the system clock to be in local time, while Linux expects it to be in UTC time, so both keep changing it. On modern Linux installs, if they detect that Windows is installed on your system, Linux will automatically configure the clock to local time to be compatible with Windows. Alternatively, you can ask Windows to accommodate Linux with this command (need admin privileges):

reg add "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TimeZoneInformation" /v RealTimeIsUniversal /d 1 /t REG_DWORD /f

GRUB can handle this. Normally, when you install Linux after Windows, this is set up automatically for you. Or you can do it after the fact. The os-prober tool is what scans your system for OS installs - you can check what it finds with this command:

sudo os-prober

And on Mint, you can use this command to update your GRUB config, which will get you the menu you want:

sudo update-grub

I think doing the above will fix it.

I think your current setup is fine, but you can change it if you want, it doesn’t really matter.
Note though that regardless of which disk you ask the Windows or Linux installers to use for their respective installs, either one will re-use the other’s EFI partition for the bootloader component. This is standard behaviour on UEFI systems. Not something to be concerned with, just something to keep in mind, e.g. if you wipe the EFI partition on your “linux disk” it will also make Windows unbootable, even though you thought you just installed Linux on the other disk.

I would try the commands I posted above and see if it works well enough: The time fix, and the GRUB/boot menu update.

Generally, it is easier to install Windows first, and then install Linux. But you may not need to do that.
Personally, I prefer to have the EFI partition on the “Windows disk” because I am less likely to want to format that… as opposed to my “Linux disk” which I like to wipe if I’m experimenting with different Linux installs.