I see these warnings and have no idea what to make of them
note: "version 2" Tectonic command-line interface activated
Running TeX ...
Fontconfig error: Cannot load default config file: No such file: (null)
warning: fmtcount.sty:10:
Invalid UTF-8 byte or sequence at line 10 replaced by U+FFFD.
warning: fmtcount.sty:22: Invalid UTF-8 byte or sequence at line 22 replaced by U+FFFD.
warning: fcprefix.sty:10:
Invalid UTF-8 byte or sequence at line 10 replaced by U+FFFD.
warning: fcprefix.sty:22: Invalid UTF-8 byte or sequence at line 22 replaced by U+FFFD.
warning: fcnumparser.sty:10:
Invalid UTF-8 byte or sequence at line 10 replaced by U+FFFD.
warning: fcnumparser.sty:22: Invalid UTF-8 byte or sequence at line 22 replaced by U+FFFD.
warning: opensans.sty:115:
Requested font "[OpenSans-Regular.ttf]/OT" at 11.99997pt
warning: opensans.sty:115: Requested font "[OpenSans-Regular.ttf]/OT" at 12.00003pt
warning: opensans.sty:115: Requested font "[OpenSans-Light.ttf]/OT:script=latn;language=dflt;" at 12.00003pt