The 878 will do APRS, both analog and DMR-APRS through the GPS revert channel, but it is not a one-button affair like the Kenwood. Almost everything worth setting has to happen in the CPS software first, then you fine tune on the radio itself. Here is the setup I actually use.
Enable APRS and GPS in CPS Options
Open the CPS, go to Tools, then Options, and check both APRS and GPS. This unlocks the APRS branch in the settings tree on the left side of the software. Skip this step and the APRS menu simply will not appear, which trips up a lot of first-time buyers.
Set Up an Analog APRS Channel
For analog APRS, create or edit a channel on 144.390 MHz, FM, and point it at your APRS RX/TX configuration under the APRS branch. Enter your callsign and SSID there, along with your digipeater path. WIDE1-1,WIDE2-1 is my default here just like on every other radio in the shack.
Set Up DMR-APRS on the GPS Revert Channel
DMR-APRS on this radio works differently. It rides on a GPS revert channel that transmits your position as a DMR data burst rather than a standard AX.25 APRS packet, and it needs an APRS server entry with a hostname and port configured in CPS. This is really built for commercial fleet tracking through BrandMeister-style servers rather than the open APRS-IS network, so unless you have a specific reason to use it, the analog channel above is the more useful one for ham use.
Configure the Beacon Interval
In the APRS settings, set a fixed reporting interval. I run mine at 10 minutes for stationary or slow-moving use. There is no true smart beaconing on this radio the way there is on the Kenwood, so if you are moving fast, shorten the interval manually or you will end up with a choppy track on aprs.fi.
Assign an APRS Key
Under the programmable function keys in CPS, assign one of the side buttons to APRS Send or APRS Info. This lets you fire a manual beacon or check your last transmitted position without digging through menus on the radio, which matters when you are trying to confirm you are actually reaching a digipeater.
Write the Codeplug and Confirm GPS Lock
Write the full codeplug to the radio, then head outside and let the GPS lock before you expect anything to transmit. Once locked, select your APRS channel and send a manual beacon using the key you assigned. Check aprs.fi to confirm the position lands. If nothing shows up, double check that APRS and GPS were actually enabled back in the Tools/Options step, since that is the single most common miss on this radio.
Related reading: What Is APRS? · Setting Up APRS on the Kenwood TH-D75A · Setting Up APRS on the AnyTone AT-D578UV III Plus