installation problem for v4.4.8

i think you may have omitted information :

our quoting upgrade instructions from 4.4.8 to 4.5.0 so im assming you ran from a command prompt:
composer update.

you dont say where you have put codeigniter and on which O.S

Anyway the upgrade instructions say, go and look for the vendor directory , then is subdirectory path something like framework/codeigniter . keep searching till you find public then copy index.php and spark and drop them into the public directory of of web dev root directory, which will repalce old ones.

to fire up it should be from a terminal :
php spark server

tjhat should fire up inbuilt server

CMS CI4 A CMS system, runs out of the box written on top of CI4

Arch Book  CodeIgniter4 on Apache(pages 92-114) 

CI4-CMS Github