Set the loudness of your audio to the level that YouTube, Spotify and podcast platforms expect, without distortion. Compare it with the original and download it as MP3 or WAV.
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LUFS measures how loud audio sounds to people over the whole track, which is not the same as its highest peak. Two tracks can reach the same peak and still sound very different in loudness. Streaming services and podcast platforms measure LUFS and turn tracks up or down to match their own level, so a track that is already at the right level is left as you made it.
Common targets are -14 LUFS for YouTube and Spotify, -16 LUFS for Apple Music and many podcasts, and -23 LUFS for television and radio in Europe (EBU R128). Platforms can change their values, so check their current guidelines if you need to be exact. The Volume Booster & Normalizer works with peak level instead, which is useful to make a file as loud as it can be without distortion.
A louder target needs a more dynamic track to be limited more. If the limiter has to lower the peaks by a lot, the sound can feel squashed, and the tool warns you. A lower target or a higher peak ceiling gives the music more room. Prefer WAV when you will keep editing the file: MP3 encoding can add very small peaks above the ceiling.