Be careful with the seagate tool.
after reading the linked page, I'm not sure it's doing what you want.
attention ! this seems it's a Windows driver, not a drive firmware option editor !
Extended Capacity Manager software installs a device driver to achieve full capacity on Legacy BIOS systems.
It messes with windows device drivers (it says the drive could be seen a 800MB instead of 3TB) due to the way intel driver will see the drive.
It edits something on windows in a form of a driver, it doesn't seem to edit the sector size's emulation mode. (advanced format -> e512)
It feels more like a workaround on software level than a proper drive hardware level modification to work on other devices than windows.
Unless it's me who didn't understand correctly, and they are talking about the "HDD firmware driver" to work on devices without BIOS system?
your issue is not a windows problem, but a sector size used by your drive.
to use MBR on a drive bigger than 2TB you need sector size bigger than 512bytes.
you need to disable the "512 emulation mode" (or e512) to expose the real sector size (4096bytes/sector).
there is a very low (bad) chance that your drive is a real 512b/sector drive. there were some manufactured drives bigger than 2TB but with no bigger sectors, resulting in only GPT compatible drives.
Most 2TB+ drives are 4096bytes now, but the drive's internal firmware has a 512byte emulation mode by default for old hardware compatibility.
instead of trying random things, maybe start checking the reported sector size of your drive? just to start on correct base to debug your problem.
not saying it's wrong, but first getting proper information before trying things which end not being the problem, and you'd do more work than needed.
maybe there are more information here (I didn't read, maybe you already know everything from here):
https://gbatemp.net/posts/6429740
too bad all the pictures are not available anymore. It's from the same user than this thread, but has different reported information.