No, Let’s Encrypt does not provide CA certificates to third parties.
If you’re seeking to start a CA that devices or software can be configured to trust, that’s achievable - there are some great free and open source software options, although it’s still a big engineering task.
If your CA needs to be publicly trusted, though, it is a serious undertaking that will need expertise and resources. The CA/Browser Forum’s Baseline Requirements are a good starting point to explore the capabilities you’ll need to have.