pages app not opening - code type X86-64 (Native)

There may or may not be any Pages related content in the local Caches folder. Are you still in Safe Boot mode, with the Finder window open on that Caches folder contents? If that window is still open on the Caches folder contents, then click in it, press command+A to select all of its contents, and then right-click to move those contents to the Trash. Then, reboot normally without attempting to empty the Trash — until after the reboot. Try Pages again, and see if it is now behaving normally.

There may, or may not be a Pages item in Caches. One that is missing is not the reason for your crashing Pages v10.3.5 issues. You did not mention if you tried Safe Boot mode, and whether Pages crashed there or not. Or if after a normal reboot, it crashed again, or stopped crashing. What happened?

You can resinstall Pages v10.3.5 a hundred times and it won't matter, because something in your installation is causing it to crash. Have you run any so-called Mac App Cleaner, or any anti-virus tool? Have you inactivated any fonts in Font Tool?

Reboot your Mac into Safe Boot mode, and see if Pages v10.3.5 works in that mode. If it does, then it is something other than Pages that is causing the crash situation. Quit Pages. While in Safe Boot mode, click on the Desktop, and then press shift+command+G to open the Go To Folder dialog. Enter the following:

~/Library/Caches

and click Go. This will open a new Finder window on your local Caches folder. Look for a file, or folder named com.apple.iWork.Pages, or something similar with the Pages icon. Move that item to the Trash, and then reboot normally. After rebooting, empty the Trash, and pressing the shift key, launch Pages v10.3.5. Did it crash again?