You have two ways to solve this issue>
1. from terminal cd to main.py location, in this case legajos_automaticos/src/, and from there, run again your command, since you already are inthe same place where the file is stored(it makes a issue diference for flet, trust me) because flet is not finding the file under legajos_automaticos.

2. form (.venv) PS C:\Users\ricar\proyectos_flet\legajos_automaticos> run the command this way>

flet run -d src/main.py

Good luck.

Jan9280