Is there a little program for conversion ?

Before that i install Windows 10 2004 i used My MP4 to MP3 program from the Microsoft Store to convert my MP4’s (which was guitar practice with a webcam) … but i fear that after the conversion to MP3 that the program can go in my system to steal my work !
So is there a little program outside Cubase to convert my video practice to MP3 ?
Is Steinberg do that or if you any advice for other safe programs !

VLC media player can extract mp3 from most video files.

If you plan to use the audio in Cubase, it would be better to convert from mp4 to wav or FLAC.
That way you have one Lossy conversion less than when using mp3, that Cubase converts to wav ( or whatever non Lossy format you have set Cubase to use internally ) anyway.