@eurodomenii - Ahhh! You ended up sending this MSI board back? If so, at least we still have a known tested and working BIOS mod from it’s use in this thread for others now 
For Aperture visibility in Asus Strix Z390-E Gaming BIOS 0805, with UEFITool 51-56, extract AMITSE/SetupData (BODY), then byte change is as shown below
Ignore “Default” info, it can be default show yes, and not suppressed, and still be hidden from user (due to however they program the “Default” itself)
This assumes you can already see >> Advanced >> System Agent (SA) Configuration >> Graphics Configuration submenu, if not then that submenu will also need unsuppressed via “Setup PE32” (As-IS) edit as shown below
*Edit - @eurodomenii << See edit below, I missed some earlier!
The one directly below this sentence also need unsuppressed too, in order to unsuppress Graphics config, since it encompasses all three settings/menus here
then each individual one has it’s own suppression also (Well at least 4G decoding and graphics config do)
Suppress If {0A 82}
0x6E078 64 Bit Unsigned Int: 0x0 {45 8A 00 00 00 00 00 00 00 00} << Change to FF
0x6E082 64 Bit Unsigned Int: 0x1 {45 0A 01 00 00 00 00 00 00 00} << Change to FF
0x6E08C Equal {2F 02}
0x6E08E End {29 02}
0x6E090 Suppress If {0A 82}
0x6E092 QuestionId: 0x2747 equals value 0xF {12 06 47 27 0F 00}
0x6E098 One Of: Above 4G Decoding, VarStoreInfo (VarOffset/VarName): 0x949, VarStore: 0x1, QuestionId: 0x327, Size: 1, Min: 0x0, Max 0x1, Step: 0x0 {05 91 84 08 85 08 27 03 01 00 49 09 10 10 00 01 00} << Search this string in hex, above it will be edits above
0x6E0A9 One Of Option: Enabled, Value (8 bit): 0x1 {09 07 9C 00 00 00 01}
0x6E0B0 One Of Option: Disabled, Value (8 bit): 0x0 (default) {09 07 9D 00 30 00 00}
0x6E0B7 End One Of {29 02}
0x6E0B9 End If {29 02}
0x6E0BB Ref: Memory Configuration, VarStoreInfo (VarOffset/VarName): 0xFFFF, VarStore: 0x0, QuestionId: 0x328, FormId: 0x2748 {0F 0F 5E 04 5F 04 28 03 00 00 FF FF 00 48 27}
0x6E0CA Suppress If {0A 82}
0x6E0CC 64 Bit Unsigned Int: 0x1 {45 8A 01 00 00 00 00 00 00 00} << Change to FF
0x6E0D6 64 Bit Unsigned Int: 0x0 {45 0A 00 00 00 00 00 00 00 00} << Change to FF
0x6E0E0 Equal {2F 02}
0x6E0E2 End {29 02}
0x6E0E4 Ref: Graphics Configuration, VarStoreInfo (VarOffset/VarName): 0xFFFF, VarStore: 0x0, QuestionId: 0x329, FormId: 0x274A {0F 0F E7 05 E7 05 29 03 00 00 FF FF 00 4A 27} << Search this string in hex, above it will be edits above
