This is thie log from the executing of the given command in Debug Console:

{"Version" : "1.1.76"} 
{"Commands" : ["list", "open [portName] [baud] [bufferAlgorithm (optional)]", "send [portName] [cmd]", "sendnobuf [portName] [cmd]", "close [portName]", "bufferalgorithms", "baudrates", "restart", "exit", "program [portName] [board:name] [$path/to/filename/without/extension]", "programfromurl [portName] [board:name] [urlToHexFile]"]} 
{"Hostname" : "Prometheus_II"} 
{"OS" : "windows"} 
downloadtool avrdude 6.3.0-arduino14 arduino keep
{"DownloadStatus":"Pending","Msg":"Downloading tool avrdude from http://downloads.arduino.cc/tools/avrdude-6.3.0-arduino14-i686-w64-mingw32.zip"}
{"DownloadStatus":"Pending","Msg":"Unpacking tool avrdude"}
{"DownloadStatus":"Pending","Msg":"Ensure that the files are executable"}
{"DownloadStatus":"Pending","Msg":"Updating map with location C:\\Users\\Samir/.arduino-create/arduino/avrdude/6.3.0-arduino14"}
{"DownloadStatus":"Success","Msg":"Map Updated"}
downloadtool windows-drivers latest arduino keep
downloadtool bossac 1.7.0 arduino keep







This is the log when trying to upload a sketch after that through the web interface:

./opt/arduino-builder/arduino-builder -compile -core-api-version 10611 -hardware opt/arduino-builder/hardware -hardware ./opt/cores -tools opt/arduino-builder/tools -tools ./opt/tools -built-in-libraries opt/libraries/latest -logger humantags -fqbn arduino:megaavr:uno2018:mode=on -build-cache /tmp -build-path /tmp/585101257/build -verbose -prefs runtime.tools.avr-gcc.path=./opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2 -prefs runtime.tools.avrdude.path=./opt/tools/avrdude/6.3.0-arduino14 -prefs runtime.tools.arduinoOTA.path=./opt/tools/arduinoOTA/1.2.1 -libraries /tmp/585101257/custom -libraries /tmp/585101257/pinned /tmp/585101257/sketch_sep17a

Using board 'uno2018' from platform in folder: /home/ubuntu/opt/cores/arduino/megaavr

Using core 'arduino' from platform in folder: /home/ubuntu/opt/cores/arduino/megaavr

Detecting libraries used...

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega4809 -DF_CPU=16000000L -DARDUINO=10611 -DARDUINO_AVR_UNO_WIFI_REV2 -DARDUINO_ARCH_MEGAAVR -DUNO_WIFI_REV2_328MODE -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino/api/deprecated -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino -I/home/ubuntu/opt/cores/arduino/megaavr/variants/uno2018 /tmp/585101257/build/sketch/sketch_sep17a.ino.cpp -o /dev/null

Generating function prototypes...

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega4809 -DF_CPU=16000000L -DARDUINO=10611 -DARDUINO_AVR_UNO_WIFI_REV2 -DARDUINO_ARCH_MEGAAVR -DUNO_WIFI_REV2_328MODE -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino/api/deprecated -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino -I/home/ubuntu/opt/cores/arduino/megaavr/variants/uno2018 /tmp/585101257/build/sketch/sketch_sep17a.ino.cpp -o /tmp/585101257/build/preproc/ctags_target_for_gcc_minus_e.cpp

/home/ubuntu/opt/arduino-builder/tools/ctags/5.8-arduino11/ctags -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives /tmp/585101257/build/preproc/ctags_target_for_gcc_minus_e.cpp

Compiling sketch...

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega4809 -DF_CPU=16000000L -DARDUINO=10611 -DARDUINO_AVR_UNO_WIFI_REV2 -DARDUINO_ARCH_MEGAAVR -DUNO_WIFI_REV2_328MODE -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino/api/deprecated -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino -I/home/ubuntu/opt/cores/arduino/megaavr/variants/uno2018 /tmp/585101257/build/sketch/sketch_sep17a.ino.cpp -o /tmp/585101257/build/sketch/sketch_sep17a.ino.cpp.o

Compiling libraries...

Compiling core...

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-gcc -c -g -Os -w -std=gnu11 -ffunction-sections -fdata-sections -MMD -flto -fno-fat-lto-objects -mmcu=atmega4809 -DF_CPU=16000000L -DARDUINO=10611 -DARDUINO_AVR_UNO_WIFI_REV2 -DARDUINO_ARCH_MEGAAVR -DUNO_WIFI_REV2_328MODE -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino/api/deprecated -I/home/ubuntu/opt/cores/arduino/megaavr/cores/arduino -I/home/ubuntu/opt/cores/arduino/megaavr/variants/uno2018 /home/ubuntu/opt/cores/arduino/megaavr/variants/uno2018/variant.c -o /tmp/585101257/build/core/variant.c.o

Using precompiled core: /tmp/core/core_arduino_megaavr_uno2018_mode_on_b3d7f87b3645115c25fed454100b3392.a

Linking everything together...

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-gcc -w -Os -g -flto -fuse-linker-plugin -Wl,--gc-sections -mmcu=atmega4809 -o /tmp/585101257/build/sketch_sep17a.ino.elf /tmp/585101257/build/sketch/sketch_sep17a.ino.cpp.o /tmp/585101257/build/core/variant.c.o /tmp/585101257/build/../../core/core_arduino_megaavr_uno2018_mode_on_b3d7f87b3645115c25fed454100b3392.a -L/tmp/585101257/build -lm

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-objcopy -O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0 /tmp/585101257/build/sketch_sep17a.ino.elf /tmp/585101257/build/sketch_sep17a.ino.eep

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-objcopy -O ihex -R .eeprom /tmp/585101257/build/sketch_sep17a.ino.elf /tmp/585101257/build/sketch_sep17a.ino.hex

/home/ubuntu/opt/tools/avr-gcc/5.4.0-atmel3.6.1-arduino2/bin/avr-size -A /tmp/585101257/build/sketch_sep17a.ino.elf

Sketch uses 1222 bytes (2%) of program storage space. Maximum is 49152 bytes.

Global variables use 22 bytes (0%) of dynamic memory, leaving 6122 bytes for local variables. Maximum is 6144 bytes.

Programming with: Serial

Flashing with command:C:/Users/Samir/.arduino-create/arduino/avrdude/6.3.0-arduino14/bin/avrdude.exe -CC:/Users/Samir/.arduino-create/arduino/avrdude/6.3.0-arduino14/etc/avrdude.conf -v -patmega4809 -cxplainedmini_updi -Pusb -b115200 -e -D -Uflash:w:C:/Users/Samir/AppData/Local/Temp/arduino-create-agent710902303/sketch_sep17a.hex:i