[arbol]

You need to terminate the TLS connection yourself so this prevents people from using DNS proxy, e.g. Cloudflare. Then you have to run a server that has a module that computes the ja3/ja4, e.g. nginx. Even then, it's possible to set your client hello in python/curl/etc. to exactly mirror the JA4 of your chosen browser like Chrome. So ja4 stops basic bots but most seasoned scrapers already implement valid ja4s/ja3s

[sequoia]

I thought it wasn't just a matter of valid but of identicalness. Multiple clients with identical JA4 which comprises if I'm not mistaken useragent but also other aspects of the host machine indicate that they are in fact a single user agent.

[arbol]

I'm sorry, I don't fully understand your question. This is what I meant by invalid: Anyone using chrome 142 has the same JA4 - I've checked across OS/devices. If you use nodeJS and set your user agent to "chrome 142" then you will have an invalid/incorrect JA4 and you'll stick out from the crowd.