This URL has it. Just pick your language. https://ftp.mozilla.org/pub/thunderbird/releases/115.12.2/mac/

The most current Thunderbird 115 ESR is Tb 115.'''14'''.0 esr. The updates are for stability and security fixes, something the older 115.12.2esr is behind on. Thunderbird 115.14.0.dmg https://archive.mozilla.org/pub/thunderbird/releases/115.14.0/mac/en-US/ other language locales https://archive.mozilla.org/pub/thunderbird/releases/115.14.0/mac/ Note unless you can update your '''macOS to 10.15''' (ten.fifteen) or later the most version recent version of Thunderbird and Firefox you can run is 115.14.0 esr and 115.15.0esr in early September may be the last unless they get extended support updates. The 116.0 or later requires macOS 10.15 (ten.fifteen) or later. Article is for Firefox though the versions apply for Thunderbird also. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support