Questions & Answers about Я искренне благодарен тебе за поддержку.
Благодарен is a short-form adjective, not a verb. It means grateful rather than I thank.
So:
- Я благодарю тебя = I thank you
- Я благодарен тебе = I am grateful to you
In this sentence, Russian expresses a state/feeling: I am sincerely grateful to you for the support.
Short-form adjectives are very common after я / ты / он / она when describing a temporary or current state.
In the present tense, Russian usually omits the verb to be.
So:
- Я искренне благодарен тебе literally looks like I sincerely grateful to-you
- but it means I am sincerely grateful to you
This is completely normal in Russian.
If you wanted the past or future, forms of to be would appear differently:
- Я был благодарен = I was grateful
- Я буду благодарен = I will be grateful