Lore hasn't concerned them on a number of things. I've defeated Rathalos in FFXIV and Monster Hunter: World, two games completely unrelated to each other with no connections in lore what-so-ever and made by two completely different game companies. And for the most part we were okay with it because we got a trial out of it and we got Behemoth in MH:W as a trade-off.
But taking that aside and you want to keep the Viera lore in tact? Males still exist in lore. They are never seen or heard of. We know that male and female Viera don't get along and the presence of the two ends in violence and females are the stronger sex here, so it just ends badly for the males.
During the events of Shadowbringers, perhaps a colony of males could be discovered, who have been completely cut off to avoid the persecution of female Viera. Or maybe even a colony where they get along, a similar principle to Red Mage lore, where there was a fringe group of Mhachi and Amdapori who put aside their differences as they recognise the violence isn't doing any good. Heck, we have beast tribes scattered all over the world who do this so we can have beast tribe quests.
They could write a side quest or series of side quests for this all. Perhaps the warrior of light/darkness helps aid them in some way in their questline and connects them to the greater world, some may find refuge in other cities, perhaps even Eorzea where their cultural clashes would not be tolerated and that these places would be safe for them. We already have stories of Xaela tribes that have had people defect and start up their own lives, some as refugees in other lands - like Sidurgu's lot, where he is the only known survivor. I roleplay a Hotgo, despite their tribe being wiped out by the Dotharl, but there were Hotgo who still lived in the lore and I chose to roleplay one such person. There are male and female tensions in certain Xaela tribes too.
In addition to this, there could also be Feols out there, who don't have that issue between males and females. We get 2 flavours of each race EG: Xaela and Raen are physically different and their lore and culture are also different.Viera and Feol would be a plausible approach.
The great thing about writing is if the lore isn't working for whatever reason, you don't even have to rewrite or retcon anything, you can write the future to accommodate what you need and you can find ways to do this and for it to feel like natural progression. Even if my ideas don't appeal, they're still give plausible reasons for male Viera and the writers of the game could surely do a better job than I?
After all, I never made it as a writer, which is why I'm a software engineer these days. So I expect they can do better than me.