Between yourself, myself, Ron Canazzi, we've all falsified both claims that it's NVDA itself (in out of the box state) or it's the synths. We've all tested 900 in digits and had them announced as nine hundred across multiple synths.
A synth will only pronounce what it's handed. There is never an instance where nine zero zero with no actual intervening point/period should have such announced barring something having been done that hands 9.00 to the synth.
This problem is idiosyncratic to the original poster's machine and ecosystem. As the fault lies there, so will the solution. The solution has a probability very close to zero of involving any given synth or NVDA in its out of the box state. It would be very easy to run the NVDA installer and create a portable copy on a USB thumb drive or even in a temporary folder on the machine of one's own creation. Running that portable version of NVDA as a test, with the same documents and using the same synth, but adding nothing else in the line of add-ons, dictionaries, etc., is an acid test for the NVDA side. Changing synths, both in the installed NVDA and portable NVDA, and comparing voice output is the acid test for the synth side.
Brian - Windows 10, 64-Bit, Version 21H2, Build 19044
You can't crush ideas by suppressing them. You can only crush them by ignoring them.