In a documentary about the Meidum pyramid, it was claimed that the Egyptians brought slaves from present-day Namibia. Is this true?

While there were slaves (of various sorts) in ancient Egypt, there is clear evidence that the pyramids were built by workers who were treated as employees, not slaves. Current thinking is that they were probably farmers who worked there when they could not be profitably working their farms.

https://www.sciencefocus.com/science/were-the-egyptian-pyramids-built-by-slaves/

It would be a lot easier to get Nubians from Nubia just up the river. Perhaps the documentary confused the two. But why use slaves who have to be fed all year when there's a work force available for part of the year that will only be up to mischief when they can't work their fields? As the link above points out, they were well fed while working on the pyramids (and provided daily with around 10 pints of beer...). While the flood was upon Egypt, there was no field work to be done - and plenty of crocodiles cruising the area where the fields had been. Judging from things like Merer's notebooks (about 4500 years old), the workers were workers, not slaves. And the above link refers to a village for thousands of workers. Not easy to run with slaves. Namibia ia a bit far off. Either way round - via west Africa (where you could buy slaves) and the length of the Med, or round the Cape, up the eastern side (where you could also buy slaves) and the Red Sea (and then overland to the Nile). I'm not considering an overland route directly to the Nile. You can sail round the other kingdoms on the coast, but overland you'd have to go through with a large party of nice fit slaves. (Unfit ones wouldn't be worth setting off with for that long a walk.) Slavery wasn't only an Egyptian or European idea. For more on Merer and Ancient Egyptian beer, see these links:
https://en.wikipedia.org/wiki/Diary_of_Merer
https://blog.britishmuseum.org/a-sip-of-history-ancient-egyptian-beer/