[Samsung Galaxy S10+ Questions & Answers] BarrettBear:
Should have known... Now that I've posted on XDA it's fixed... In-case anybody else is having trouble here are the steps I've written down for myself.

Phone is S10+ SM-G975F (beyond2lte) - Bootloader / OEM Unlock is already unlocked.

******************************************************************

FLASHING STOCK ROM (ALWAYS GOOD PLACE TO START):

******************************************************************

1. Phone into Download mode (Vol Down + Bixby button, insert USB (Don't use power button))

2. Odin, AP in AP, BL in BL, CP in CP, CSC in CSC (NOT the HOME one). USERDATA stays EMPTY!

3. Phone may restart/erase several times, in the end inbuilt recovery will turn up. Use this to factory reset.

4. Wait for it to continue like normal after factory reset.

5. Setup INCLUDING with WiFi. WiFi REQUIRED. No need to add your account

6. Make sure OEM Unlock is still checked.

*************************************************************************************************

ROOT INSTRUCTIONS: https://www.thecustomdroid.com/samsung-galaxy-s10-root-guide/

*************************************************************************************************

1. Use adb push to shunt over Magisk Manager (download latest one), and the "AP" file

2. Install Magisk Manager

3. Open, select install, make sure "Recovery" is ticked, next, select "Select and Patch a File"

4. Select the AP file, then click "Let's Go"

5. Use adb pull, as the MTP file transfer ****s up the large patched files :( Thanks Microsoft!

6. (adb reboot bootloader) Restart phone in Download mode

7. Open Odin, & flash the patched Magisk AP file in AP, BL in BL, CP in CP, CSC (NOT the HOME one) in CSC.

8. Let device reboot while holding POWER, BIXBY, and VOL UP, and release all 3 buttons on bootloader warning screen.

a. NOTE: If you end up with a bootloop, hold POWER, BIXBY, VOL UP until you enter the built-in recovery menu, and do a factory reset.​

9. Set device up like normal, remember to enable the WiFi

a. Check device internal storage, should be XXX out of 128GB (Or whatever you have)​

10. Search installed apps for the Magisk one, it won't have a proper icon to begin with

11. Open it, and continue the setup as it instructs. It’ll reboot the phone.

12. Device is now rooted.

********************************************************************************************

TWRP INSTRUCTIONS: https://www.thecustomdroid.com/samsung-galaxy-s10-twrp-magisk-root-guide/

********************************************************************************************

Phone must be rooted for this to work!

1. Copy the un-magisked file "twrp-3.5.2_9-3-beyond2lte.img" onto phone

2. Open Magisk, select install, make sure "Recovery" is ticked, next, select "Select and Patch a File"

3. Patch the "twrp-3.5.2_9-3-beyond2lte.img" file

4. Copy that patched file onto your PC, and rename it magisk_patched.img

5. Open powershell in same folder, and type

a. mv magisk_patched.img recovery.img​

b. tar cf twrp-beyond2lte.img.tar recovery.img​

6. Enter into Bootloader mode

7. Load up Odin, untick auto-reboot, and put the magisk-patched TWRP.tar file in AP

8. Press PWR and VOL-DOWN to exit Download Mode, as soon as screen goes black, switch to PWR, BXBE, VOL-UP, release PWR & BXBE when you see bootloader warning, keep VOL UP

9. In TWRP, swipe to allow modifications

10. Flash multidisabler-samsung.zip

11. Go to wipe - format data - yes, after go back to TWRP home screen

12. Click Reboot > Recovery (NOT SYSTEM), you now have a TWRP enabled device.

13. Reinstall Magisk, and check root status, it should ask you to do the whole re-download/5 second reboot thing because you did the wipe > yes thing in TWRP.

UPDATE

: After restarting my phone I lost root (Magisk was still installed, but it didn't have an "installed" version listed). To get past this I...

*************************************************************************************************************************

Magisk reinstallation via TWRP:

https://xdaforums.com/t/rom-signatu...or-s10e-s10-s10-exynos.4173663/#post-83658967

*************************************************************************************************************************

1. Copy the "beyond2lte-boot-magisk.img" onto phone (see URL above)

2. Run Magisk, patch the "beyond2lte-boot-magisk.img" file, then copy it over onto your MicroSD (I just find it easier)

3. Boot into TWRP > Install > Install Image button (Bottom Right)

a. If TWRP has vanished, follow steps above to get it back​

4. Flash the patched file to "Boot"

5. Go to TWRP Home screen > Reboot into Recovery (not into System)

6. Check Magisk Manager should have Root again (Don't update Magisk via app though, or you’ll bollocks the whole thing up, and have to start all over from the start.)