the, IPA /ðə/ before consonant sounds, /ðiː/ before vowel sounds. One spelling, two spoken forms.
The e stays silent as a letter; it only signals the vowel sounds /ə/ and /iː/.
She opened the door. Say /ðə/ before the consonant sound of door.
She ate the apple. Here /ðiː/ links smoothly into the vowel of apple.
Write it the every time, even when you say /ðiː/. The spelling never changes, only the spoken vowel does.
Before a vowel sound you may hear /ðiː/, but the spelling stays t-h-e. The longer vowel lives in speech alone; no letter is added or changed.
Thy and thee are separate archaic words, not spellings of the article. Thee means you and ends in the long vowel /iː/, which is why it sounds like the strong form of the but is written differently.
Before a vowel sound you may hear /ðiː/, but the spelling stays t-h-e. The longer vowel lives in speech alone; no letter is added or changed.
The th here is always the voiced sound /ð/, never the voiceless /θ/ of think. Both Cambridge pronunciations, /ðə/ and /ðiː/, share that same voiced start.