Oven question and cheese

I am familiar that cheese needs a hechsher because of the gezeira of gevinat akum. My question is: is someone cooks this kind of cheese in the oven, am I able to also cook in that oven after them, even though they used this cheese. Also, is there any of issue of chametz with this cheese?

There is no problem using oven. I’m assuming that the cheese was in a pan/pot.

No Chometz issue

Can I cook something dairy uncovered at the same time as someone cooks matza pizza uncovered with the cheese I pictured above that does not have a hechsher?

If it’s in the oven, you shouldn’t put your food in. If it ahead happened and it was below or on same rack, you can eat it.

ok. but if I don’t cook them at the same time, it is permitted for me to put my natza pizza in the oven after this person put there’s in the oven?