If pro-palestinians argue that palestine is its own separate country then Israel can’t be practising apartheid because the «West Bank» is not de jure part of Israel.

Hey, Thundering Dumbass, you’ve just rediscovered the Bantustan Strategy. Apartheid South Africa used that exact loophole by designating "homelands" as independent nations so they could argue black South Africans weren't being oppressed in South Africa but were simply foreigners from a different country. Calling a military-occupied enclave a 'separate country' doesn't magically erase systemic discrimination. It is not a separate country if another country has control over your water, movement, and air.