What are the current options for a Non-B visa holder seeking a visa run in Thailand amid border closures?

You have to keep an open eye to all countries in the area for changes. At the moment you may have the option to apply for a new Non Immigrant B Visa in:

Yangon Myanmar.

Vientiane or Savannakhet in Laos but need medical statements from Thai hospital

You know your nationality, so check this updated page which country you can and are able to visit before 7 th April

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I don't think you can do a land border run anymore sadly.

depends on your nationality where and how you can go to another country. But so far no news any Royal Thai consulate/embassy in SEA stops issuing visa.

apply for the Extension of Stay at your local immigration Office and when not possible, it will be a difficult way to find a Thai Consulate for a new Non B visa

Think you can extend your current b visa at amy immigration place. Think you get 1 month but maybe 60days

>I heard that most of the borders are now closed

Not true

>My Non-b visa will expire next month 7th of April

Is this a single entry visa, a multiple entry visa, or an extension of stay based on employment?

>knows a border that still open for visa run

There's a lot of borders still open. But April 7th is a long way away.

> I have documents from my company for the non b application

My advice is for your company to issue an extension of stay based on employment. However, my crystal ball isnt' working, and I don't know which borders would be open by then.