Losing my interest learning when I reach near to finish line

I can't even watch anything outside of udemy for even 10%. My problem is I don't know why I'm getting bored after reaching 70-80% of the course.

I'm learning a lot till I'm <50% of the course and slowly, I stop learning at that rate, and at 80%, I totally stop learning at all and get bored having to learn.

Why is this happening and how can this be fixed?

Would investing my money into giving certification exams fix this issue? I'm learning about computer networking, systems administration, databases, distributed systems, system design, packet sniffing etc. Not all at once, obviously.