Apple has done this multiple times because loan rates were/are cheaper than paying taxes to repatriate cash.

I know less about shareholder buybacks than I do about divideds, but they are pretty similar to dividends. A buyback is returning $X in bigger chunks to a few shareholders, and a dividend it returning a $X to all shareholders. A dividend usually drops stock value in line with amount of dividend paid out, so in a sense you could think if it as the company saying "I'm buy 1% of your $100 share, so you get $1 and the share is now worth $99".

Anytime a company pays a dividend AND increases their outstanding debt in the same time period, you could draw ths conclusion that they financed the dividend using debt.

Check out the financials for Vector group...

https://finance.yahoo.com/quote/VGR/financials?p=VGR

On the summary page you can see they pay about a 15% dividend. On their income statement you can see their net income is less than $100 million USD. On the balance sheet, you can see the long term debt has increased by a serveral hundred million over the last few years. That dividend sure sounds like it is financed by debt, although you'd have to dig into what is really going on to know for sure.