What are the best options for doing a visa run from Thailand to Malaysia for a French citizen?

Avoid the agency they’ll over charge go by yourself

From. Nakhon we have been several times to Kota Bharu consulate. Drop the application in on a Sunday and its back Monday afternoon. Penang is nice for a visit however visa applications can take 3 days. Kota Bharu you can get the early Train from Nakhon to Sungi Kolok and go across the border to Malaysia and get a taxi to Kota Bharu. If you arrive early enough lodge the form then hotel overnight collect your passport the next day at 2 pm

I dont think you need a visa agent to do a visa run. You just have to go to the next country then return.

I think the questions you should be asking, which are the best embassies to get tourist visas.

It used to be Vientiane or Penang.

Your uncle will go to some place with an embassy. File some paperwork. Wait a day or two or three, pickup the passport, return to Thailand.

Different embassies require different paperwork, have different policies and different turn around time.

The other consideration is getting back into Thailand.

The Penang border crossing used to require tourist to carry 20,000 baht. It was a strange requirement but when I crossed - they asked for it.

Probably a good idea your uncle travel with all paperwork and 20,000B cash.

It might help to specify what type of visa he has currently and what type of visa that he would like to obtain while in Malaysia?