mGBA 0.8 beta 1 has been released which finally implements most features that Nightly builds of the emulator received over the last few months. In its changelog, we find mention of:
GameBoy Colour palettes have been added to original GameBoy games
Experimental XQ audio support which provides higher quality audio in games using the GBA’s standard sound engine (Sappy) – more info at bottom of this page
Better debugging tools including a frame inspector
The ability to use the Switch’s internal brightness sensor for a game titled Boktai
Ability to load RetroArch-style cheat files in CHT format
The unlicensed Wisdom Tree Game Boy mapper is now supported
L2/R2 and L3/R3 can now be mapped on the PSTV
Dynamic display resizing is now supported on the Switch