Monotone speech usually comes from giving every word equal weight. Natural speech changes speed, volume and pitch depending on meaning. You can design that contrast without sounding theatrical.
Underline one word per sentence
Choose the word that carries the point. Slow down slightly before it and give it a little more energy. If five words are emphasized, none of them feel important.
Pause after meaning, not punctuation
A written comma does not always need a spoken pause. Pause after a useful claim, before a contrast and before the final line. Give the viewer time to process.
Change speed on purpose
Move faster through setup and slower through the core idea. Record one practice take with exaggerated contrast, then reduce it by half for a natural final result.