Being ethno-nationalist has its own ramifications. At least Tadjikistan openly declared support for the 'national resistance front of Afghanistan' led by the tadjik Ahmed Massoud, son of Ahmed Shah Massoud known as the best guerilla fighter/leader of the 20th century, during the war against the communists. But the Talibans gave fierce warnings about repercussions unless they ceases support and over time decreased to when the rebels lost momentum.
Uzbekistans and Turkmenistans border closed their border when the Talibans took over, not even giving opportunity to Uzbeks or Turkmens to cross the border, lol. They also began working with Talibans immediately afterwards too. So much for ethno-nationalist unity, I bet Somalis would do the same too
Pakistan are the ones who've built up the Talibans. During the Soviet/Afghan war, they supported Talibans since India, their rival, sided with the monarchs/communist/secular rulers. Once the US overthrew them, Pakistan gave refuge to Talibans and freely crossed the border between the two countries. Without Pakistan, they would've not been able to re-group post-invasion.
Also, Pashtun live in both Pakistan and Afganistan and they don't recognize the borders as they claim that it was made by colonials. Even by the Taliban til this day. Not different from Somalis

But you're right. It was elite Punjabis that supported Talibans due to India's support for the other side, and the locals being against it. Now the elites are regretting too given their the aftermath in the country.