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

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.