This was Bayern's line-up, with the substitutions and their times:
Ulreich - Pavard (Sarr 46), Upamecano (C. Richards 46), Nianzou (Lawrence 46, Scott 63), Stanisic (O. Richards 46) - Goretzka (Cuisance 46), Musiala (Rhein 46) - Gnabry (Arrey-Mbi 46), Sané (Vidovic 63), Coman (Choupo-Moting 9, Sieb 63) - Lewandowski (Tillman 46)
As you nca see, Coman played for only 9 minutes, and all the other senior players were subbed off in the second half, except for Sané who played until the 63th minute. Here's also when the goals were scored:
0-1 Osimhen (69), 0-2 Osimhen (71), 0-3 Machach (85)
So you can't really say with a straight face that Bayern lost 0-3 to Napels playing a good part of its starting 11.