Is there some plan to release Thunderbird 102 to testing or stable in near future?
It will come when it reaches Arch stable - then the as-always flow on Manjaro - not sooner and not later - it will be there when you see it.
Thunderbird version 102.0 is only offered as direct download from thunderbird.net and not as an upgrade from Thunderbird version 91 or earlier. A future release will provide updates from earlier versions.
Please search before posting. This has been asked a few times before.