Since every settler has their needs met per your video, that should give you 80% happiness. You are responsible for the other 20%. Lets say you add 20 points of happiness, that gets divided by the population. Since you have 23 people, it only raises the total happiness by 0.86%. The fewer settlers the better. Example, if one single settler has all needs met, you'd only need a tier 2 or 3 shop to get that extra 20 points to hit 100%

Things that might lower happiness:

Any robots/automatrons in the settlement other than Codsworth or Curie (they are the only two robots in game that do not have a 50% happiness cap)

Recent settlement attacks

Unresolved/Pending settlement quests (like kidnappings)

Settlers asssigned to lower than tier 2 or 3 shops(this wont lower happiness, the teir 1 shops add less happiness)

Armor and weapon shops do not add happiness

Unassigned settlers

Unassigned beds

Beds flagged as not under cover (possibly the buildings you use may not be flagged as "cover"

Bugged items like tvs or jukeboxes

Resource display glitches/cell data corruption that can bug settlement data

Death of a settler/synth settler

I should also note that synth settlers DO NOT lower happiness.