Find all domains under a TLD

The information you seek isn't openly available. However, there are a few options you can try:

You might want to try inquiring at the respective registries directly about getting access to the Zone files. However, the process can take weeks and some registries choose not to offer access at all. For newer GTLDs you can apply at ICANN's Centralized Zone Data Service. You might need to provide a good reason to access the full lists. The Zone file can only be pulled once a day, though, so for more up to date information the only option is a paid service.

Whois API offers the entire whois database download in major GTLDs (.com, .net, .org, .us, .biz, .mobi, etc). It also provides archived historic whois database in both parsed and raw format for download as CSV files, as well as a daily download of newly registered domains.

A similar, popular question exists already but the answers and links are a bit outdated.