When was Flash Video encoder last released?
What was the last version?
According to the end-of-life page, All Apps Help | Products and technical support periods , the last version released was 3.2 on 6/12016. End of extended support was 9/1/2016.
Note that Flash Media Encoder is a completely different product from Flash Player. Since the product has reached EOL, there is no forum for Flash Media Encoder.
There is a chance that you're talking about Adobe Media Encoder, and asking when was the last version that could make FLV files. If that's the case, it was the Media Encoder that came as part of Flash Pro CS6. If you have a Creative Cloud subscription that includes Adobe Animate, you can use the CC menu and under Animate you can choose to see older versions. Install Flash Pro CS6 from that list, and you will get the last version of Media Encoder that can make FLV files.