if conditions
 

what are the vBulletin 5 if condiitons to place in the new page manager

I'm not sure what you mean, but many of the conditions listed in the vB4 Conditions article should work.

Not working in vBulletin 5 page manageR!

That gives nobody any information so noone will be able to help you. You need to be waaaaay more explicit on what you are doing, where you are doing it, and what you have tried and what the result was if you want any help.

it's too sad that THIS_SCRIPT is no more valid!
how to check if it's main page then?

I believe you could use the $nodeid for a page.