To avoid merge conflicts, we haven't been writing changelog entries for Certbot 2.0 PRs. We'll need to go back and do this retroactively before the 2.0 release. More info at #9354 (comment).

• The default key type for new certificates is now ECDSA secp256r1 (P-256). It was previously RSA 2048-bit. Existing certificates are not affected.

• Certbot no longer supports versions of ACME from before the RFC 8555 standard.

• acme and Certbot no longer support the old urn:acme:error: ACME error prefix.

• The Apache plugin no longer supports Apache 2.2.

• Removed the certbot-dns-cloudxns plugin.

• Certbot will now error if a certificate has --reuse-key set and a conflicting --key-type, --key-size or --elliptic-curve is requested on the CLI. Use --new-key to change the key while preserving --reuse-key.

• 3rd party plugins no longer support the dist_name:plugin_name format on the CLI and in configuration files. Use the shorter plugin_name format.

• acme.client.Client, acme.client.ClientBase, acme.client.BackwardsCompatibleClientV2, acme.mixins, acme.client.DER_CONTENT_TYPE, acme.fields.Resource, acme.fields.resource, acme.magic_typing, acme.messages.OLD_ERROR_PREFIX, acme.messages.Directory.register, acme.messages.Authorization.resolved_combinations, acme.messages.Authorization.combinations have been removed.

• acme.messages.Directory now only supports lookups by the exact resource name string in the ACME directory (e.g. directory['newOrder']).

• Removed the deprecated source_address argument for acme.client.ClientNetwork.

• The zope based interfaces in certbot.interfaces have been removed in favor of the abc based interfaces found in the same module.

• Certbot no longer depends on zope.

• Removed deprecated function certbot.util.get_strict_version.

• Removed deprecated functions certbot.crypto_util.init_save_csr, certbot.crypto_util.init_save_key,
  and certbot.compat.misc.execute_command

• The attributes FileDisplay, NoninteractiveDisplay, SIDE_FRAME, input_with_timeout, separate_list_input, summarize_domain_list, HELP, and ESC from certbot.display.util have been removed.

• Removed deprecated functions certbot.tests.util.patch_get_utility*. Plugins should now
  patch certbot.display.util themselves in their tests or use
  certbot.tests.util.patch_display_util as a temporary workaround.

• Certbot's test API under certbot.tests now uses unittest.mock instead of the 3rd party mock library.