My Garmin DriveAssist 50 outputs full HD baseline MP4 videos with constant bitrate that is slightly higher than 8 Mbps. As with all dashcam videos, the quality is not something to get excited about but it isn't too bad either. My standard process is simply to re-cut these videos to throw out idle time (e.g. while parked). Since I don't really use them for further editing, compression settings are a bit on aggressive side.
I start by customizing
Internet HD 1080p profile as it has most of configuration as I want it. What I do change is Profile level by simply increasing it to High. I consume there videos on my PC and there is simply no reason I could think of to go lower. And yes, High profile works on mobile phone too.
Dashcam videos lend themselves quite well to MP4 compression so I went with average variable rate of 6 Mbps. For moments when a bit more action is happening, a maximum of 8 Mbps should suffice. Note that I use two-pass encoding here in order to squeeze a bit more quality despite lower bitrate. This does double the encoding time but I find it reasonable compromise.
I also uncheck progressive download support as I don't intend to stream these and this does give a few more bits to encoder.
Lastly, as my camera doesn't record sound, I turn the audio off.