Question about Sensirion SCD4x CO2 Gadget

Yes, but unfortunately only via app and Bluetooth, not via USB.

And you can't save it as a file, at least on Android, because the app immediately opens the "Share with"/"Send to" dialogue.

The destination then receives a ZIP file containing a file in EDF format (extension .edf, the file header says "EdfVersion=4.0", which is probably https://de.wikipedia.org/wiki...). This seems to be a TSV (tab-separated values) format.

Yes, the EDF format describes a structure in an ASCII file that can be opened with any text editor:
# EdfVersion=4.0
# Date=2024-01-30T14:24:50.479139
# ApplicationName=Sensirion_MyAmbience
# ApplicationVersion=3.2.0 (83)
# OperatingSystem=ios
# SensorFamily=MyCO2
# SensorId=A5:A8
# SensorName=ritz.AirQ
# Type=float64,Format=.3f,Unit=s Type=string Product=MyCO2,Device=MyCO2,Unit=ppm,Sensor_Serial_Number=A5:A8,Type=float,Signal=Carbon Dioxide
Epoch_UTC Local_Date_Time CO₂
1663439764.6 2022-09-17T20:36:04.638260 0.000
1663439769.7 2022-09-17T20:36:09.684560 536.000
1663439775.2 2022-09-17T20:36:15.229184 529.000
1663439780.3 2022-09-17T20:36:20.274792 534.000
1663439784.3 2022-09-17T20:36:24.299123 525.000
1663439789.3 2022-09-17T20:36:29.350212 522.000
1663439793.9 2022-09-17T20:36:33.886496 518.000
1663439803.5 2022-09-17T20:36:43.479754 517.000
1663439808.0 2022-09-17T20:36:48.031817 515.000

A CSV file can be created from this, for example by replacing the spaces with ";".