ATtiny1616

PlatformIO

Install VSCode or VSCodium and then install the PlatformIO project.
Open the plugin and then import this project.
Don't have to use platformIO but that might be the easiest way to set up things.

sudo apt install python3-pip -y
sudo pip install pymcuprog
Free up UART to be used for UPDI connection. Add dtoverlay=disable-bt to the end of /boot/config.txt
Disable UART outputting to console: Remove console=serial0,115200 from /boot/cmdline.txt and reboot.
Ping sudo pymcuprog -d attiny1616 -t uart -u /dev/serial0 ping
Erase sudo pymcuprog -d attiny1616 -t uart -u /dev/serial0 erase
Program through UPDI sudo pymcuprog -d attiny1616 -t uart -u /dev/serial0 write -f ./Blink-attiny1616.ino.t1616.20c0.mD0.v261.hex
Note that you should Erase before programming each time, I think..