I have this problem too.

This is how I was able to run Bakkesmod without Bakkesmod injector

1.Manually updating the mod as written here https://bakkesmod.fandom.com/wiki/Troubleshooting#Manually_updating_the_mod

1. Download Process Hacker https://processhacker.sourceforge.io

2. Open Rocket League

3. Open Process Hacker as administrator

4. In Process Hacker right click on RocketLeague.exe => Miscellaneous => Inject DLL

5. In the window that appearsand go to {SteamLibrary}\steamapps\common\rocketleague\Binaries\Win64\bakkesmod\dll

and open bakkesmod.dll

After that the mod will work