If you mean namecheap doesn't support letsencrypt DNS-01 challenge, you can still buy your domain in namecheap but point your NS somewhere else that support DNS-01 challenge (e.g. cloudflare, Route53, or even Google Cloud DNS).
Most letsencrypt clients uses HTTP-01 challenge though, which doesn't care about who's hosting your dns.
I tried to reason with Richard [CEO who says to be 'open' to user input], but I didn't even get a robotic response.
The truth is that the web environment is totally corrupted and the domain registration process seems like something under the control of the mafia. A refoundation of the network is in order.
Disclosure: The domain is registered on the excellent and unbiased Registro.br [unfortunately below the top level .com]. Namecheap allowed me to create aucky.live and aucky.app. I want my aucky.com. (*)The service proper is in the making.