CTRL+SHIFT+O will only 'Open message in Conversation if an email has already been selected.

ADDITIONAL: Have you got 'threaded' view enabled ? If yes, then to use CTRL+SHIFT+O, you need to expand the thread first.

re : I can't search Search Method ? eg: Global Search or Quick Filter search or 'Find' > Search Messages'

It would be useful to know: what OS are you using Windows 10, MAC, Linus etc ? what version of Thunderbird are you currently using?

Please state all the steps - state precisely what you are selecting and what process you use. Also tell us what occurs and what you see. Tell us any error messages you get.

Open in Conversation only works if the Global search and Indexer is enabled in Settings/General (at the bottom). If it's already enabled, try rebuilding the search index.

Open in Conversation only works if the Global search and Indexer is enabled in Settings/General (at the bottom). If it's already enabled, try rebuilding the search index.

Thank you!

It works :)

Steps to Rebuild the Global Database

   Quit Thunderbird.
   Locate the global-messages-db.sqlite file in your Thunderbird Profile.
   Delete the global-messages-db.sqlite file.
   Start Thunderbird. The re-indexing process will start automatically. Depending on the number of messages, it might take some time for the indexing to complete. You can continue to use Thunderbird, but performance might be affected and search will return only partial results or even no results until the indexing is complete. The indexing progress can be monitored through the Tools > Activity Manager menu.