D-Link DSL-2750U

i got a D-link DSL-2750U (hardware version U1) router which is not connected to internet, i dont have a internet connection, i use internet from my mobile, i couldnt find how to redirect my mobiles internet through router to rest of my devices, now im thinking of installing open wrt, i found the firmware for D-Link DSL-2750U C1, will this work?

Well, the "original" device is already too small for Openwrt and with barely supportable broadcom wifi.
Can you try to get boot logs at most detailed level and post the link where you would download working firmware update to same OEM version you have installed?

i dont know much about this stuff, im not using openwrt its current firmware is from the dlinks website, sry for my english, i just want to redirect my internet from my phone to the router and then to my other devices through lan from the router

Cannot guess hardware specs from you eyes only.
I know that you are not using OpenWRT. I want to understand if your device is that much better than other release to be supported by OpenWRT ever. The actual support involves programming and soldering on your part in case such is viable.

the hardware version on the router pages says U1, i couldnt find any other info

One is clear it was never supported.
Since you have this antiquity in hand you are only one able to browse its web configuration interface. Somewhere in most advanced options there is log message level, set that to maximum output amount (debug/verbose or something like that), then restart device and find where you can download system logs.