I think you should reevaluate your very concept of "official", high detailed source for all country borders worldwide.
For a really "official" source, you would have to check 200 +/- official sources of all +/- 200 existing countries wordlwide. Borders are defined on a bilateral delimitation between two neighboring countries, there cannot be an "official" registry of all worldwide borders, but at best +/- 200 "national" datasets. There is not international body (like UNO) registering the official definitions of all conturies, this is strictly a matter of bilateral agreements - and in many cases still of custom and practice (customary law) - at least for a precision of less then 100 meters and in more remote areas (deserts, swamps, forests, mountains, lakes etc.).
So every insititution that collects these date (as OSM) is not an official source any more by definition. If you really are to get official definitions, you can get them only at the national level.
In many cases, not even that does help much. Neighboring countries often have diverging definitions of what belongs to them and what to their neighbors. Georgia and Russia will have different definitions on their borders - not to speak about Crimea. There are many other cases: the delimitation of the borders between Uzbekistan, Kyrgyzstan and Tajikistan in the Ferghana valley has been an issue for decades now. We not only speak about clear cases of contested territories, but also of generelly undisputed portions of the border that are not delimited - thus no unanimously shared definition in the terrain (like boundary stone) does exist. Only if both parts sign an agreement that fixes a border in all it's details (most often still based on real boundary stones put in the terrain by a bilateral commission) can we speak about an "official" border. As border zones tend to be a delicate issue for security concerns, many states ar not keen to publish official documentations about this delimitation. And a map in always all cases is a derivative product that documents one kind or another of border-definitions, but it is not the definition in itself - so to get the "official" source would meen going to the archives (if you have access)...
And even today, many borders are not defined in such a precise way, but are still based on older principles like "in the middle of the river" - riverbeds change, however. There are sections of the border between Switzerland and Italy that are defined as "the ridge of a glacier". With climate change and melting glaciers, the border changes, too. As well, there is no agreed definition of the border between Switzerland and Germany in the Lake of Constance - as there is no need for it:
there is no legally binding agreement as to where the borders lie between the three countries. See: https://en.wikipedia.org/wiki/Lake_Constance#International_borders
So if even in the middle of Europe with it's sophisticated administrative institutions, high precision cartographic technologies and centuries-long tradition of border delimitation borders sometimes are still not defined to this day "on the meter", this is even more true for many parts of the world.
So I'm not sure if the very concept you're after does makes sense. With no dataset you'll get a guarantee that it is correct or generally accepted. The more "official" and detailed the data gets, the more you'll get an illusion of precision and accuracy that in fact does not exist.