Why is the Krebs cycle considered a part of aerobic metabolism if molecular oxygen is not involved in any of the reactions in the cycle
Oxygen is actually not needed in the Krebs cycle - it is needed in the electron transport chain that is downstream of the Krebs cycle to regenerate NAD+ from NADH. NAD+ is a co-enzyme and acts as an electron carrier in oxidizing reactions at various positions in the Krebs cycle. However, note that without O2, NADH accumulates and the cycle cannot continue as it needs NAD+ to run.
Krebs cycle - No O2 needed:

Electron transport chain - O2 needed to regenerate NAD+ essential for the Krebs cycle: