the Basic rule in islam is , EVERY sexual act between a girl and non-mehram is haram, and it will be one Form of Zina as it Involves sexual pleasure between each other and unlawful touching.
Prophet Muhammad said in one hadith:
The eyes commit Zina, the hands commit Zina and feet commit Zina and
the genitals commit Zina." (Musnad Ahmad, Hadith no. 4258)
So the general ruling is, Stay away from Every sexual act, doesnt matter if it actually means Zina or not. as Allah says in Quran
[17:32]And do not come near to adultery, it is a shameful deed and an
evil, and opening the road to other evils.
Allah says DO NOT COME NEAR, he does not say Stop from it, dont come near to it. and act of rubbing covered genitals together give enough sexual pleasure that it is Highly likely that it will lead to intercourse, nobody is strong enough to resist that temptation.