Manual decryption of (old?) files from external storage

Nextcloud version (eg, 20.0.5): 23.0.0
PHP version (eg, 7.4): 7.4

Hello,

As I was browsing support forum I see that major versions are released but encryption feature stays as immature as it was years ago. OK, forgive me my bitterness, I am just tired of all that kung-fu.

So, I had external folder where I had some files. Some were already there at the moment I attached storage, some I added. Encryption was ON. I do not remember which version I had, maybe 16, maybe 17. Some time ago I upgraded my instance all the way to 23. And recently I realized some of encrypted files were not properly converted. I cannot say if rest was converted or if they were not encrypted at all, I know that now I have several files I cannot access. Unfortunately, 1-2 of them are really important for me and I would like to restore them.
Opening in webapp does not work, I have error 500 and error in logs “Cannot decrypt this file, probably this is a shared file. Please ask the file owner to reshare the file with you.”
With one file I tried to copy or delete etc, so probably system lost knowledge it is encrypted and now it opens normally as a encrypted content - that’s I want to use ‘external’ way.
Could it be related to fact I changed my password in the meantime? It would be weird.

So, I have encrypted file (content is like “HBEGIN:oc_encryption_module:OC_DEFAULT_MODULE:cipher:AES-256-CTR:signed:true:HEND”…).
I have content of data/files_encryption/ folder:
OC_DEFAULT_MODULE with master_, pubShare_ and recoveryKey_ files
keys/files where i have OC_DEFAULT_MODULE with fileKey and user.shareKey files
These files seems to be in old(?) format - small size and binary content, not hex like for new files.

Is there any way how may I manually decrypt my files? Some script, openssl command, whatever?
Do not tell me to use “occ”, I played dozen times with encryption: enable, disable, scan, migrate etc. Still files are encrypted.

Thanks for any suggestion.