Umbral sight doesn't make or break this build. So even if they got rid of it, things will be fine.
My caution on using the linked build is that it puts a 17 in dex, but doesn't suggest a half feat to bump it to 18. Which is probably because there isn't a good one in bg3 other than resilient which we don't need here.
If you care about skills and or even if you just want more consistent damage, start with rogue 1 then gloom 5. This will get you sneak attack for 5 levels then extra attack at 6 rather than nothing for 4 levels until extra attack at 5.
Crossbow expert is up in the air now since we already have the BA attack on an offhand hand crossbow and you can double up on cool secondary bonuses from magical ones. Plus they seem to have taken out the loading property for everyone.
I'd do these stats:
12 14(2) 13(1) 10 14 10
You can toss the 12 wherever you want. But this spread will let you use your ranger powers decently and keep you from failing as many skill checks since you dont have a dump stat.
I would take the familiar from the ranger so you can always have an ally granting you sneak attack. The raven is great for blinding enemies and can get next to any target you want early on in a fight.
We don't know what ranger 6 will get us yet so this may change, but if you really want to alpha strike your enemies I would do:
Rogue 1/ Gloom 5/ Assasin 2/ Battlemaster 4.
This will get you the most dice to toss on turn 1, one Dex ASI the Sharpshooter feat, and the fun superiority die.
If somehow ranger 6 is amazing, take the level from battlemaster. Or maybe even go ranger 9 so you can keep the ASI, get 3rd level spells and the wisdom save proficiency.
If you go with the battle master hand crossbow build you could chuck out 4 attacks that are all crits on your first surprise round. So something along the lines of 8d6 weapon damage, 4d6 sneak attack, 8d8 superiority die, 2d8 gloomstalker bonus +40 sharpshooter + 12 from your dex (probably don't get the 4 for your offhand crossbow). Maybe throw some poison or fire on your x-bows to start with an even bigger bang.
I dont remember if Hunter's Mark alerts enemies or not, but if it is sneaky, then you can solo a young dragon before it knows you exist.