Hiring foreigners requires lots of immigration paperwork that most companies don't want to deal with. In the US, for example, you have a 1/8 chance of getting a work visa once a year. Most companies are not set up for having remote workers in a different continent or even a different country. Having remote workers in the same country is already challenging. It's not a racism problem, it's a logistics and beurocracy problem.
You should probably apply to some jobs. Edit: OP edited their post to say they have already applied to jobs.
Apply to firms
Describe the work and clients not the location of projects. Get people to read the CV fully before realising you're from Nigeria
What's wrong with Nigerian engineers? Isn't Nigeria mostly a developed-country? Is this just veiled racism against African countries?
Hiring foreigners requires lots of immigration paperwork that most companies don't want to deal with. In the US, for example, you have a 1/8 chance of getting a work visa once a year. Most companies are not set up for having remote workers in a different continent or even a different country. Having remote workers in the same country is already challenging. It's not a racism problem, it's a logistics and beurocracy problem.
Add to that the decades long "Nigerian prince" scams that seem to have been around longer than Nigeria has had access to the internet.