But research also shows that they often miss what remote workers gain in productivity in harder-to-measure benefits like creativity and innovative thinking.
what 引导的宾语从句还原回去就一目了然了。宾语从句中的主语是 they，谓语 miss，宾语是 what 从句。
but 在这里是连词（或称副词连词）。张道真《现代英语用法词典》P174：
（3）开始一个句子，表示意思上的转折（可译作“但是”，“可是”）
But that question doesn't arise. (Snow)
But I'm not going to argue with you tonight. (Priestley)
You may think I am exaggerating. But I can assure you that these figures are correct. (DEU)
There will be still difficulties. But they can be overcome. (Mis)
"I'll give you £5." "But that's not
enough!" (DCE)
再举个《经济学人》里的句子：They are now worth more than $100bn each.
But their routes to these highs look quite different.
