Opening an MBTiles file offline can be quite difficult. However, with MapTiler Engine, this is a standard feature. Simply double-click on any mbtiles file, and you will immediately see the content. You can also use Engine to merge multiple tilesets very easily.
After previewing your tiles, it is possible to directly upload them to a MapTiler workspace or to other cloud providers. You can also host your MBTiles on your own on-prem or offline infrastructure with MapTiler Server.