Being from Nigeria does not bar someone from filing or being approved for naturalization. The reports about “extra vetting” don’t change eligibility to file an N-400. Naturalization is not an entry benefit it’s governed by different INA codes (which is the authority used for travel bans). So the travel-ban framework doesn’t control N-400 eligibility. Yes, we are seeing some interviews get canceled or rescheduled, but from everything I have witnessed and again I might be a little off here, that appears to be more about additional due diligence than any change in eligibility. (things are changing daily)
We recently filed an N-400 ourselves, and honestly, it was probably the easiest form in the whole process. The requirements are very clear. Under the 3-year rule, you just need to show that you’ve been married to a U.S. citizen for three years, that you’ve been living together in marital union during that time, and that your spouse has been a U.S. citizen for the full three-year period. The evidence is pretty straightforward if it’s a bona fide marriage — citizenship proof, green card, joint taxes, lease or mortgage, joint bank accounts, insurance, etc.
My suggestion would be to go ahead and start drafting the N-400 online. I’m almost certain you’ll be pleasantly surprised by how simple it is. And if you do get stuck, this forum and its members are an incredible resource. The only caveat I’d add is that if there’s anything questionable in his background, then it’s worth seriously considering an attorney. Otherwise, this is very doable on your own.
Wishing you nothing but the best