In the TI Resource Explorer if navigate to the Sitara MCU+ Academy for AM243x - 1.00.00.04 -> Getting Started -> AM243x MCU+ SDK Getting Started Guide, it actually opens a document for AM64x MCU+ SDK.
E.g. as shown in the following screenshot:
It looks like this is just a wrong link in the Sitara MCU+ Academy for AM243x - 1.00.00.04.
The correct AM243x Getting Started Guide is at https://dev.ti.com/tirex/explore/content/mcu_plus_sdk_am243x_08_00_00_21/docs/api_guide_am243x/GETTING_STARTED.html
