nut package doesn't have modbus support enabled
Network UPS Tools (NUT) is a package for Uninterruptible Power Supply management. Since NUT v2.8.0, drivers for several new UPS models, including generic_modbus, phoenixcontact_modbus, huawei-ups2000, socomec_jbus, and adelsystem_cbi are added (I'm the author of one of the drivers). However, the use of these drivers requires an external library libmodbus installed and the build option --with-modbus
switched on when building NUT.
On Alpine, NUT currently doesn't have Modbus support enabled. Thus, users of Modbus-based UPS systems cannot manage them on Alpine via NUT.