Infrastructure Too Low Problem

Your options on how to deal with Level 1 infrastructure are limited. Either you can go around them by land, bypass them by sea, or upgrade them to Level 2 or better (which may take 5 years of research before you can build a dirt road). Be aware that if you do circumvent or bypass those low-infrastructure provinces, your supply lines will still go through them, making operations beyond them nearly impossible unless you use convoys to supply a port that happens to be further along the chain of supply. If it's NOT in the direct line, those supplies will simply return overland to your capital.

I think he/she means that you cannot enter a province with infra level 1 means you cannot conquer it, no matter how strong your forces are. As you cannot conquer it, no supplies will go through it also.
Additionally to bypass it by sea is to modd or just accept it as yes, infr IS low in Africa even nowadays the mighty USA cannot control a desert area...

The way to take the British in Africa is to grab the ports and work inwards, not to march inland first. Cut off their supply, as you grab the territory around no pass zones it will become yours in which case you can then upgrade it later if need be, but likely wont have to. The key is the ports....

There are a couple of "walls" of Level 1 Infrastructure which prevent forces from moving all around the African continent. Most of the Level 1 Infra provinces will change hands if you occupy the higher-level provinces adjacent, but a few seem to be designed to prevent movement. Your choices are either to gain control of them by occupying their "controlling" neighbor and then upgrade the infrastructure, or else go around them.

Historically, most of those areas were considered "impassable" and "uninhabitable" by any sizable force or population, either due to horrific terrain, disease, near-total lack of food and/or drinkable water, or all of the above.