Thunderbird's desktop export and Thunderbird android's import does not support contacts.

The best approach tends to be carddav. For example https://support.mozilla.org/en-US/questions/1347462 and https://www.reddit.com/r/Thunderbird/comments/wvqs24/one_way_carddav_address_book_synchronization/

Thanks, Wayne. In fact, my needs are very simple: I very seldom have to send an email from my phone to someone in my address book other than a reply to an email received. Nearly all my emailing is done on my Windows PC. So far I have a decidedly low-tech solution: a Word file listing all my correspondents, stored on my phone; I can then simply copy an address if necessary. That file will obviously have to be updated every so often.