Not correct working php 7.3

Hello, can it be, that it does not work properly? I have it on my staging page which is identical to the real page installed and there is php 7.2 unfinished working fine. On the real page miz php 7.3 not. The navigation a, b, c, d ….. is not there. I still disabled all plugins. Without success. I wanted to buy the pro version. But as long as that does not work. Thanks alot ciao Rusty