Text in PowerPoint lives inside boxes, not flowing freely like in Word.
Click a "Click to add title" or "Click to add text" placeholder and type directly into it. Drag its edges to resize the box.
A slide with more than roughly six lines of text usually reads as a wall of text from the back of a room. Short phrases, not full sentences, keep a slide readable at a distance.
By default, PowerPoint shrinks text automatically to keep it inside its placeholder — typing more than it can comfortably hold makes everything smaller rather than overflowing the box. This is exactly why "too much text" quietly becomes "too small to read" instead of visibly breaking the slide.