I also have this problem. I've gone through all the recommended checks, and in fact the blynk-ser.sh script loads up and starts to cycle properly. The board is an Uno Wifi rev 2. I'm running macOS Big Sur beta, and some days ago had success uploading to an Uno (not Wifi). Here's my upload messages:
Arduino: 1.8.13 (Mac OS X), Board: "Arduino Uno WiFi"
Sketch uses 9212 bytes (28%) of program storage space. Maximum is 32256 bytes.
Global variables use 395 bytes (19%) of dynamic memory, leaving 1653 bytes for local variables. Maximum is 2048 bytes.
/Users/press/Library/Arduino15/packages/arduino/tools/avrdude/6.3.0-arduino17/bin/avrdude -C/Users/press/Library/Arduino15/packages/arduino/tools/avrdude/6.3.0-arduino17/etc/avrdude.conf -v -patmega328p -carduino -P/dev/cu.usbmodem143302 -b115200 -D -Uflash:w:/var/folders/x3/8mq7t3fj3h95_4q1nxzm2yv80000gn/T/arduino_build_820518/Button_-_Serial_USB.ino.hex:i
avrdude: Version 6.3-20190619
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2014 Joerg Wunsch
System wide configuration file is "/Users/press/Library/Arduino15/packages/arduino/tools/avrdude/6.3.0-arduino17/etc/avrdude.conf"
User configuration file is "/Users/press/.avrduderc"
User configuration file does not exist or is not a regular file, skipping
Using Port : /dev/cu.usbmodem143302
Using Programmer : arduino
Overriding Baud Rate : 115200
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00
avrdude done. Thank you.
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.