I just got introduced to PayloadCMS via youtube live called
"The Future of CMS: An Inside Look at Payload with Founder James Mikrut"
The Node ecosystem as a whole appears to be moving to TypeScript, which is why all of our examples are in TS. We decided to have all of our documentation in TS since it was too much of a burden to maintain both TS/JS - especially when it appeared 90% of the people interested in Payload were using TS.
You can still use Payload with vanilla JS, you may just have to strip out the types from the code in the documentation