Understood. Main concern with that scenario is passport renewal may take longer than my extension date (2 months from now) so that would mean no extension possible. Would prefer to just extend visa on old passport, then renew passport before January and take it from there. Thanks!

ok thanks. Maybe leave the thread open a bit longer in case some offer further advice.

But after I renew the passport, don't I just transfer the visa extension to the new passport with same time validity? It's a one-year extension.

I will renew my passport by mail to Bangkok Embassy. They say up to 6 weeks, which could interfere with my extension. So again the main question is: can I do a (1 year) non-O visa extension with a passport valid less than 6 months? Thanks

Most travellers use Non Khai / Vientiane or Chiang Khong / Huay Xai. Are they "closed"? Nope, not yet.

555 I said checkpoints, not borders ;-)

Which one(s)? There are several Thai/Laos border checkpoints.

The closest land crossing to Laos from Chiang Mai which is open to international travelers is Chiang Khong / Huay Xai. But again you need a Laos visa which can be obtained on arrival for a fee.

But let's be absolutely sure about the Mae Sai / Tachilek thing first.

^Because continuing to apply for repeat tourist visas + extensions after nearly 4 years of "living" here could be seen by consular or immigration officials as abuse of the system, resulting in denial. Just saying, they might (and often do) check social media profiles. Many of us played that game in past years, but it's getting more risky. Advice not accusation.

Facebook profile says "Lives in Chiang Mai"

Might want to remove that, as your visa history suggests a fake tourist ;-)