Is AMP still a ranking factor on Google?

No but It was designed to enable publishers to load content on their websites more quickly on mobile devices. Most of the people using smartphones for searching.
No Way, AMP stand for Accelerate Mobile Pages. The AMP Project is an open source initiative that embodies the vision that publishers can create mobile-optimized content once and have it load instantly everywhere. So We found that AMP pages load four times faster and use eight times fewer data than traditional mobile-optimized pages. It makes your webpage faster to device friendly and googles index fastly.
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