Birthright was another one of those #dnd settings that fall under "great concept, bad rules". The idea of player characters starting out as the rulers of their own domain was and is awesome (although I've grown a bit leery about the whole "Divine Right of Kings" thing - but I can let that slide for a good story). However, the rules for managing domains and fighting armies were a mess, and would involve more spreadsheets than I want to bother with for recreational gaming.
If I were to run a #ttrpg campaign in this setting, I'd probably use @GregStolze@mastodon.social 's Reign (with bits of Wild Talents thrown in for the birthright powers) - rules for running domains (or "companies") are integrated into the ruleset from the start, and they are also much more scaleable - if you plan to conquer all of Anuire, this should be much less of a headache.
Although I'd have to re-read the assorted magic rules of Reign to see if they have something similar in mood to what *Birthright offers (which is mostly D&D magic, but with some significant thematic differences from more "standard" campaign settings).
