Allow combined UTF-8 characters for filenames on Nextcloud External local storage files

On Nextcloud v 27.1.0 I have an external storage of type local.
Having file names with utf-8 character encoding and combined character with combining diaeresis fails to be shown.

The error is shown like the following:

php occ files:scan -p /myPath/myExternalStorageFolder
Starting scan for user 1 out of 1 (me)
        Entry "klaus/Hans hätte besser aufgepasst.mp4" will not be accessible due to incompatible encoding
.
.

For example the letter 'ä' can be represented in two utf-8 complaint forms:

• (U+00E4), hexadecimal representation: c3a4
• or a combined form of the character "a" (U+0061) followed by combining diaeresis (U+0308), which is used to add two dots above a character. Hexadecimal representation: 61cc88.

Using the latter method for filenames results in an error due to "wrong" character encoding, even though it is valid UTF-8 character encoding.

Consider a scenario where you have a Spanish keyboard as a German tourist in Mallorca. You may produce a combined UTF-8 character for the letter 'ä' using such a keyboard to name your holiday videos and store them on your memory stick right there.

This report highlights the improvement request.

a workaround:

A tool called 'convmv' is available for Linux and can be installed with the following command: sudo apt install convmv

To correct filenames on your holiday memory stick, following my example, use the following command for a dry run:

convmv -r -f utf-8 -t utf-8 --nfc  ./myPhantisticHolydayMemories/*

This command will show what files would be renamed without actually renaming them. After inspecting the actions it would take, you can perform the renaming with the following command:

convmv -r -f utf-8 -t utf-8 --nfc --notest ./myPhantisticHolydayMemories/*

Once you have completed this process, trigger a scan again using:

php occ files:scan -p /myPath/myExternalStorageFolder

You should no longer encounter any "incompatible" encoding errors.

Start by reproducing the issue with a decomposed UTF-8 filename in an external local storage and run php occ files:scan -p /myPath/myExternalStorageFolder. Trace the external-storage scan path that reports the filename as having incompatible encoding. Done when valid combined UTF-8 filenames are accepted and shown without that error.