You have discovered why up grading from one OS ( stretch ) to the next in the series ( buster ) is not recommended,
you cant guarantee what the out come will be due not knowing what software is installed and how it will be affected by the up grade.
That's why the recommended up grade route is to do a fresh install of the the new OS and then reinstall all your software and just copy over any data or programs you might have written.
The chances of getting your SD card to boot your new pi4 are slim at best and you are on your own as no one here will know what software you and install or how you configured it.
We want information… information… information........................no information no help
The use of crystal balls & mind reading are not supported