Indeed we do not yet support TypeScript 3.9, as our analyzer is built on top of eslint parser and we are presently working to overcome some performance regression with the last versions of eslint, the versions bringing support for TypeScript 3.9.
However, you may still be able to analyse your TS code files and receive warning such as:
WARN: You are using version of TypeScript XXX which is not officially supported; supported versions >=3.2.1 <3.8.0
This means we are not blocking the analysis, we are not skipping the files: analysis could however fail in some cases with unsupported TS version: i.e. parsing problems. As said, work is in progress with no defined ETA yet - so for the moment, if you seek maximum stability, I would suggest not to analyse files on unsupported TS versions.
Cheers,
Daniel