Is Thunderbird 78 still safe?

Hi, By coincidence I found out that apparently Thunderbird got an overhaul a while back on is now version 91.0.3. My install on Windows 10 is on version 78.13.0. I regularly check for updates using Thunderbirds own update checker but it doesn't update to V91. According to this article that's expected behaviour: [https://www.thunderbird.net/en-US/thunderbird/91.0/releasenotes/ Thunderbird version 91.0 is only offered as direct download from thunderbird.net and not as an upgrade from Thunderbird version 78 or earlier. A future release will provide updates from earlier versions.] This is fine for me but I want to know if V78 is still safe and does it still receive security updates? Or do I need to reinstall to V91 for that? Thanks in advance.