(xGM210P dev board, Studio 5, Gecko SDK 3.0)
At the top of that page it says "This version works with Simplicity Studio 4 only" and refers to docs for later versions of the Gecko SDK. But then, there's no documented analog for Gecko SDK 3.0.
I need an app (pretty quickly) that will enter test mode, issue "sl_bt_test_dtm_tx(test_pkt_carrier, 0, 0, tes VidMate t_phy_whatever);" but after a few days of experimenting I've not succeeded. I've only a few days' experience with these tools and libs. Can someone help me with an app.c that accomplishes this?
v3.0 documentation on docs.silabs.com is still in progress. Until it's ready I suggest you read the official DTM documentation for v3.0, it may help: https://www.silabs.com/documents/public/application-notes/an1267-bt-rf-phy-evaluation-using-dtm-sdk-v3x.pdf
If you want to migrate this example from v2.x to 3.x: https://docs.silabs.com/bluetooth/2.13/code-examples/applications/implementing-wireless-direct-test-mode-dtm then I suggest you reading the migration guide: https://www.silabs.com/documents/public/application-notes/an1255-transitioning-from-bluetooth-sdk-v2-to-v3.pdf