How does sloeber ide set {serial.port} on upload?

I have problems uploading my sketch using sloeber-ide 4.4.0.202107110422 and ATTinyCore 1.3.3. using the Diamex AVR USB ISP programmer on Ubuntu 21.10.

In the project properties page I have set the port to /dev/ttyACM0. It is shown in the project view correctly and the sketch builds as expected using one-click right out of the IDE.

But uploading fails with:

Launching: /home/felix/Packages/Sloeber/arduinoPlugin/packages/arduino/tools/avrdude/6.3.0-arduino17/bin/avrdude -C/home/felix/Workspaces/Arduino/hardware/ATTinyCore-1.3.3/avrdude.conf -pattiny85 -cstk500v2 -P{serial.port} -Uflash:w:/home/felix/Workspaces/playground/arduino/atiny_test_02/Release/atiny_test_02.hex:i 
Output:
avrdude: ser_open(): can't open device "{serial.port}": No such file or directory

avrdude done.  Thank you.

The execution of command "avrdude" is done.

Somehow the IDE doesn't set {serial.port} correctly: Triggering the upload via cli using -P/dev/ttyACM0 works fine.

Is this a bug somewhere or a misconfig in my installation? (I am pretty sure that this was working two years ago...) Uploading sketches directly to an Arduino nano using /dev/ttyUSB0 works as expected.

It would be convenient to trigger the upload with one click, too. Any idea where I could look into / how to fix it? Thanks for reading!

You're in the wrong forum. This is NOT the sloeber forum.

@missdrew many here use Sloeber and the author is a moderator in Netherlands section