The LTEbee adapter board you linked above was a special product we developed in 2019 for interfacing the Digi-brand LTE cellular boards with the Mayfly Logger. The Digi board have been nearly impossible to buy since late 2020 because of production/shortage issues with the manufacturer and aren’t expected to be back in stock anywhere until later this year supposedly. So we designed our own LTE cellular board which we called the EnviroDIY LTE Bee (https://www.envirodiy.org/product/envirodiy-lte-bee-pack-of-5/) and that new cell board was specifically designed to work with the Mayfly v1.0 board with no adapter needed between them.
The assembly manual we published a few years ago describes the process of using a Mayfly v0.5b board and the older Digi boards with the adapter, so your confusion is understandable. We’re currently rewriting the manual to include photos and instructions for all the new hardware that was released a few months ago, including the new Mayfly and new LTE cell board. I’m not sure of the exact release date of the updated manual, but it should be really soon.