Yes, you need to declare on your US tax return interest income generated from keeping money in a Thai bank, which is often a requirement for obtaining and maintaining a long-term extension of stay in Thailand.
Yes, you may be able to claim a Foreign Tax Credit for any taxes actually paid to Thailand on this interest income.
No, you cannot claim the Foreign Earned Income Exclusion (FEIE) on this interest income because it is specifically not "earned" income.
These answers are further explained at the following links:
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