Going forward, all the new meta-plot content are for V5 and unless otherwise stated in new content, old meta-plot is still valid. V5 scales the game back to young vampires and, in my opinion, has done away with most of the bloat in favour of elegant simplicity but not without some serious blunders. You can still use all the new V5 meta-plot for V20 or previous editions (and vice versa) and even mix and match the rules as the V5 core book encourages bending or Homebrewing the rules as you see fit, which I like very much.
Well no, you can't just use 5E as the base ruleset and then tack on the v20 lore because the developers of 5E are gonna be shilling for the 5E lore to come along with the ruleset since it resonates with their new ideology. Btw the meta-plot of 5E has some seriously retarded changes like: the Sabbat are just...gone. Gone where? Well they just fucked off somewhere and aren't mentioned at all. The new Sabbat book only allows for Sabbat NPCs. Not to mention how they used the various clans to fit their new woke agenda: the Brujah are now hipster BLM/antifa characters, the Ventrue are basically Trump-supporters, the Malkavians are pussified versions of their old Clan with many of their "controversial" disciplines gone, etc.
I played 5E fairly recently with my friends and we used v20 lore for it. It still sucks in many other regards and we shifted back to v20 entirely. The developers however wouldn't be up for using 5E rules with v20 lore. Of course they're going to promote the lore that's tacked on the system they're using, it's a promotion for the tabletop itself. It's like saying BG3 should use 5E rules but 2E lore.