Small crack at the top of the newly replaced window, does the window need to have a lintel?

I would have to inspect further but maybe yes

Good evening, it happens that after the installation of the windows and the related repairs, cracks appear due to the large space between the lintels and the window or due to its lack.

Very rare on a first floor window On removal of the old window you can crack the existing render as usually rendered around the window so easy to damage or crack existing render

I would get a structural engineer to have a look but I would personally say no if it hadn't had one with the old windows it shouldn't need one now but always best to get it inspected just to be sure, alot of times people can be rough removing the old windows (sometimes can't be helped if old ones were wooden) but this can cause plaster and brickwork to crack hope this helps