I remember when Itachi did it to Sasuke when he was dying it was supposed to be a special brother gesture and now it's being spammed like hell and doesn't feel special anymore .Heck the emotional attachment is non existent cOmpared to back then
It's lost significance simply because Sasuke, Sarada, and Sakura use/think of it in the wrong ways. Even while being Itachi's brother- Sasuke doesn't really have a right to use it. Doesn't even seem like he understands it even after Itachi explained the meaning to him- otherwise he wouldn't use it.
Itachi explained that he loved Sasuke and as a result wanted to keep him out of the Uchiha/Konoha conflict. He wanted him to be ignorant in bliss and innocent, trying to enjoy life after he got his initial vengeance. The forehead poke isn't meant to be inherently positive.
This trademark was dropped with Edo Itachi- when the Uchiha bros received closure and the elder brother finally came clean. He told him a very very brief summary of the truth, apologised and said there was no need for Sasuke to forgive him, and brought their foreheads together/practically hugged him to show that he no longer viewed Sasuke as an object to protect but an equal capable of making his own decisions, a brother he will love no matter what his decision.
^Every reader, pairing fan or not, could relate to this as long as they had the most basic reading comprehension and it warmed their heart, even if just a little.
Meanwhile, with Sasuke and Sakura- the latter does not know the meaning. It's confirmed given her reactions that she knows nothing about Itachi. This "trademark" of Itachi's is only a way for SS to say "look, Sasuke is being romantic". And it really shouldn't be. It was initially for tragic familial love. Kishimoto should have kept it the same. It's not meant to be paralleled to a kiss. lol, by this logic I guess that Sasuke had romantic feelings for his elder bro and it was a mutual thing.

Yeah... not romantic.
And as for Sakura using it on Sarada- the initial meaning is still not known. And to any reader, it's pretty evident that Kishimoto just paralleled Sakura to Itachi this chapter in order to get people to hate her less in this Gaiden. Low ponytail (when did she grow out her hair and why did she cut it lol? Every other panel has her with short hair and this showed Sarada at one point as an 8 yr old Academy student... Sakura had long hair in this chapter but back in 700 she did not?), "maybe next time", the way she smiled with her eyes closed is similar to Itachi's death scene, and of course the poke itself. /Too bad this failed given quite a few on other sites that are not hardcore Sasuke/Sakura/SS fans are raging and saying Itachi was disrespected with this chapter.
However, with all this being said- this was still my favourite chapter of Gaiden since it was still sweet to see how Sakura loves Sarada. Though, the writing would be better if the SSS family had their own trademark and Kishimoto had the characters being original imo.