Most of the advice about ad lazyloading you find online is either outdated, oversimplified, or just plain wrong if you actually care about viewability and money. This post is based on the pain of building a real lazyloading library from scratch, testing it in production, and seeing what works (and what doesn't) with Prebid.js and modern web ads.
There are two ways to create a custom Prebid.js bidder adapter. Using "registerBidder" from bidder factory It is the recommended way and it is covered fairly well in the official docs here: How to Add a New Prebid.js Bidder Adapter. The process is straightforward and simple, so I don't see much value in repeating it here. If it fits your goals, just follow the official guide and stop reading further :) Using "registerBidAdapter" method from public api