Plain and simple. craft the essence for regeneration, made condensed potions using them. tried them out in the field ( all of them), but was not given any potion effect at all.

Forge: 1.16.4-35.1.37
Reliquary: 1.16.3-1.3.4.1061 (which is the newest available though it says it supports 1.16.4)

I have just tried this and I am unable to recreate your issue, I just get the effects applied? Are you playing with it in a pack? if so it's likely another mod causing this or interaction with it. if you can figure out which one I can take a look if there's anything that Reliquary is doing wrong here.

Nuclear Craft, Astral Sorcery, Bookshelf, Enchantment Description, Reliquary(obviously), Apotheosis, ObserverLib,JEI, Forge, ToroHealth, CuriosAPI, Xaero's Mini-map, Waystones, Xaero's World Map, Placebo, and Storage Drawers.

That is all the mods installed up to latest versions.

any of these conflict. I know I have had problems with ToroHealth in the past with model rendering bugs.

So this still isn't resolved. can find no conflicting mods that would negate any condensed potions. so they just dont work.

I have actually just retested in dw20 pack and they work correctly. I am guessing you thought they don't because they don't show particles, but that's a feature that you don't see those annoying circles in your view all the time. However you can still see the effects in player's inventory view.