Fldigi is a computer program intended for Amateur Radio Digital Modes operation using a PC. Fldigi uses the PC sound card as the main means of input from the radio, and output to the radio. These are audio-frequency signals. The software also controls the radio by means of another connection, typically a serial port.
Fldigi is multi-mode, which means that it is able to operate many popular digital modes without switching programs, so you only have one program to learn. Fldigi includes all the popular modes, such as DominoEX, MFSK16, PSK31, and RTTY.
Fldigi looks doesn't look that complex, but it supports quiet some modes.... and has a lot of settings...
You can use Hamlib to connect to the rig.
The Ham Radio Control Libraries, Hamlib for short, is a development effort to provide a consistent interface for programmers wanting to incorporate radio control in their programs. Hamlib is not a complete user application, rather, it is a software layer intended to make controlling various radios and other shack hardware much easier.
Fldigi doen't auto start a rigctld daemon. So you start rigctld before running fldigi...
So maybe using RigCAT is a better solution for the moment.
Search for your rig sound card.
Audio Tx level
The audio Tx level can be adjusted in the bottom right part of the main screen.