The toolchain for the new ATtiny 0-series and 1-series is not up to date in a lot of package repositories. Most of these errors have been fixed upstream, but I have included minimal versions of the patches here.
Fixed with patches/ldscript.patch.
Apply this to /usr/avr/lib/ldscripts/avrxmega3.xn.
The exact path may be slightly different for you.
This patch is from the forums, not upstream.
/usr/avr/include/avr/io.h:583:6: warning: #warning "device type not defined" [-Wcpp]
583 | # warning "device type not defined"
Fixed with patches/devdef.patch.
Apply this to /usr/avr/include/avr/io.h.
The exact path may be slightly different for you.
main.c:115:9: error: 'MCUCR' undeclared (first use in this function)
115 | set_sleep_mode(SLEEP_MODE_STANDBY);
| ^~~~~~~~~~~~~~
Fixed with patches/sleep.patch.
Apply this to /usr/avr/include/avr/sleep.h
The exact path may be slightly different for you.