Counting the number of suttas is really difficult, and impossible to do with 100% confidence. The problem is that many suttas are abbreviated due to repetition, and there is no clear path to expanding them all in full. For example, for just one text, the Samyukta Agama in Chinese, we have three different sutta counts depending on edition:
- Taishō: 1362, based on the mistaken order after the filing error.
- Foguang: 1359, after correcting the order and removing Asoka.
- Yin Shun: 13,412, likely the most original, based on the three aṅgas.
The Pali would show no less variation. If we are counting genuinely different, substantive texts, I’d say a couple of thousand. But if they were all spelled out in full, some tens of thousands.
However, as @Gabriel_L pointed out, this idea rests on a verse by Ānanda, and it is not really sure what he is referring to here. Probably it just means “countless teachings”.