The default Nikkah gift is money in a card. There is nothing wrong with it. It is useful, it is expected, and it will be forgotten by the following spring.
If you want to give something the couple actually remembers receiving, the trick is to stop buying for the house and start buying for the marriage.
Why most wedding gifts miss
Almost every Nikkah gift falls into one of three piles: money, something for the kitchen, or something decorative for the new home.
All three are aimed at the household. But a new household assembles itself fairly quickly — within a year the couple will have bought whatever they were missing. What does not assemble itself quickly is the relationship.
Early marriage is mostly two people discovering how much they assumed about each other. The gifts that land are the ones that help with that.
Give them something to do together
The most useful thing you can hand a newly married couple is a reason to sit down opposite each other with no screen involved.
intention. was built for this — a Muslim couples conversation card game made with Muzz. 100 cards for two players, with questions drawn from Quran and Sunnah, plus Wild Cards and a "Dig Deeper" card for when an answer is clearly holding something back.
It works as a gift for a specific reason: it does not require the couple to already be good at talking about difficult things. The deck does the asking, which removes the awkwardness of one person having to raise the subject.
Give them something they will keep separately
Not everything should be joint. Two people who reflect on their own tend to arrive at conversations better prepared.
A guided journal each is an unusual Nikkah gift and a genuinely good one — particularly for a couple who have just moved from a lot of family around them to a much quieter house. The Self & Faith Journal works if they are the reflective type; The Faith In Five Journal if realistically they have five minutes and no more.
Give something that marks the date
Anything engraved or dated gains value purely by surviving. A pen is the most-used object in this category by a wide margin — The Faith Pen is engraved with "He Who taught by the pen" (Quran 96:4) and comes boxed, which matters more for a wedding gift than people admit.
Two of them, given as a pair, is a quietly good gift.
What to avoid
Anything that implies advice. Marriage guidance books given at a Nikkah are received as a comment, however they were meant.
Anything large. Many couples move at least once in the first two years. Furniture and big decorative pieces become a logistics problem.
Anything requiring assembly or a specific wall. It will stay in the box.
Duplicates of the obvious. They will receive several prayer mats and at least two Quran stands. Assume the obvious is covered.
On the money question
If money is the custom in your family, give the money. Do not fight a cultural expectation over a gift.
But add something small alongside it. The envelope covers the obligation; the small thing is what gets remembered. A card game and a handwritten card costs very little next to the envelope and does entirely different work.
The short answer
If you want one gift and want to stop thinking about it: a conversation card game for the couple, a pen each, and a card you actually wrote.