It’s actually something that is changing in English right now. In some languages like German all word-initial vowel sounds are pronounced with a glottal stop at the start (a so-called “hard attack”) but English generally doesn’t (or didn’t) do that, resulting in “thee apple”. Younger speakers are starting to use hard attack before word-initial vowel sounds so the “thee” variant isn’t present for them.

I’m not sure if this also affects “a” vs “an” (i.e. I don’t know if younger people are starting to say e.g. “a apple”) because that obviously makes an orthographical difference so it might be more persistent. Although I suppose they coud say both “an” and begin the next word with a glottal stop.

Keep an ear out if you’re listening to a younger native English speaker and you might be able to hear it.