Workedaround by commenting out all references to M5StamPLC and M5Tab5 (some are bypassed by #ifdefs and don't have to be deleted):

Arduino: 1.8.19 (Linux), Board: "M5PaperS3, Disabled, OPI PSRAM, QIO 80MHz, 16MB (128Mb), Core 1, Core 1, Hardware CDC and JTAG, Enabled, Disabled, Disabled, UART0 / Hardware CDC, 16M Flash (3MB APP/9.9MB FATFS), 240MHz (WiFi), 921600, None, Disabled"

/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:83:12: error: 'board_M5StampPLC' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
 { board_t::board_M5StampPLC   , GPIO_NUM_15,GPIO_NUM_13 , GPIO_NUM_1 ,GPIO_NUM_2  },
            ^~~~~~~~~~~~~~~~
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:148:12: error: 'board_M5StampPLC' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
 { board_t::board_M5StampPLC   , GPIO_NUM_7,  GPIO_NUM_8,  GPIO_NUM_9,  GPIO_NUM_10 },
            ^~~~~~~~~~~~~~~~
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:167:12: error: 'board_M5StampPLC' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
 { board_t::board_M5StampPLC   , GPIO_NUM_21 },
            ^~~~~~~~~~~~~~~~
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp: In member function 'void m5::M5Unified::_begin(const m5::M5Unified::config_t&)':
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:1237:19: error: 'board_M5StampPLC' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
     case board_t::board_M5StampPLC:
                   ^~~~~~~~~~~~~~~~
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp: In member function 'void m5::M5Unified::_begin_spk(m5::M5Unified::config_t&)':
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:1554:21: error: 'board_M5StampPLC' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
       case board_t::board_M5StampPLC:
                     ^~~~~~~~~~~~~~~~
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp: In member function 'virtual void m5::M5Unified::update()':
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:1821:21: error: 'board_M5Tab5' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
       case board_t::board_M5Tab5:
                     ^~~~~~~~~~~~
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:1953:19: error: 'board_M5StampPLC' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
     case board_t::board_M5StampPLC:
                   ^~~~~~~~~~~~~~~~
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp: In member function 'void m5::M5Unified::setTouchButtonHeightByRatio(uint8_t)':
/home/wsanders/Documents/ArduinoSketchbook/libraries/M5Unified/src/M5Unified.cpp:2044:19: error: 'board_M5Tab5' is not a member of 'm5::board_t' {aka 'lgfx::boards::board_t'}
     case board_t::board_M5Tab5:
                   ^~~~~~~~~~~~
exit status 1
Error compiling for board M5PaperS3.


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