Android adopted/internal memory SD card

I made a big mistake and was using an SD card as internal/adapted memory
in my 50 euro Chinese Coolpad 1851 (Mega 5) android 8.1.0 phone.

And, of course, at some point the card got corrupted, and it is not
read by the phone anymore. The phone works and the card itself works,
it can be read by software.

But of course the card is fully encrypted and when read externally nothing useful
can be done with the card, and my last backup was 2-3 months ago.

I see on the internet that I have to extract the encryption key from the phone
stored in /data/misc/vold and then mount and decrypt the card to get
access to the files. There are nice instructions and it seems easy.

The thing is that the phone is not rooted, to get access to the filesystem
to read the key, and I don't want to mess with it.
I don't care if it gets bricked, but I don't want to risk to lose the
encryption key. I guess it is not mandatory to be root to read files,
but at the same time I cannot install any new programs, because the
internal memory does not work (it waits for the missing SD card).
And I don't want to install a new SD card as internal/adapted, because I
am afraid the key to the previous one will be deleted.

I am looking for a way to read the encryption key,

thank you