Version history:
Ethiopian languages, like Gəʿəz, Tigre, Tigrinya, Amharic, are typeset using the AbyssinicaSIL font which has the widest support for Ethiopian languages at the time of this writing (August, 2021).
AbyssinicalSIL: 9.35 pt ~ Brill 11 pt
AbyssinicalSIL: 8.5 pt ~ Brill 10 pt
AbyssinicalSIL: 7.65 pt ~ Brill 9 pt
The Abyssinica SIL font is distributed under the SIL Open Font License, so its use (among other things) is free.
The type size of AbyssinicaSIL text should be 83% of the size of surrounding Brill typeface text.
Windows fonts, as long as they are TrueType fonts (.ttf) or TrueType Collections (.ttc), or CFF-flavoured OpenType fonts (.otf) can also be used on macOS.