Set your reduction amount to between 6dB and 12dB . Do not try to remove 100% of the noise. Remove 80% of it. A tiny bit of ambient noise sounds natural; a totally dead vacuum sounds fake. A Word of Caution (The "Lasagna" Principle) Here is the golden rule of noise reduction:
If you apply noise reduction to a vocal track, then render it (bounce it), then import that rendered track into a new project and apply more noise reduction... your audio will turn into mushy, warbled garbage. reduce noise plugin
Most plugins have a "Delta" or "Listen" button. Press this. You will hear only the noise being removed. If you hear bits of voice or reverb tails in there, your settings are too aggressive. Set your reduction amount to between 6dB and 12dB
Stop talking/playing. Let the room tone play for 3-5 seconds. Highlight that section and tell your plugin to "Learn" or "Capture" the noise floor. A tiny bit of ambient noise sounds natural;