Join splitted -001.mkv files with bash

I have some -001.mkv files splitted in this way

the rings + of power-001.mkv
the rings + of power-002.mkv
..

nightmare.return-001.mkv
nightmare.return-002.mkv
..

I need to join -001.mkv files to obtain files like this

the rings + of power.mkv
nightmare.return.mkv

I thought of such a code, but doesn't work

for file in "./source/*001.mkv;" \
do \
    echo mkvmerge --join \
    --clusters-in-meta-seek -o "./joined/$(basename "$file")" "$file"; \
done

source is the source folder where -001.mkv files are located
joined is the target folder

Can you try this?

for f in ./source/*-001.mkv
do
    p=${f%-001.mkv}
    echo mkvmerge --clusters-in-meta-seek \
        -o ./joined/"${p##*/}".mkv "$p"-*.mkv
done

Given your example, the for f in ./source/*-001.mkv should loop though nightmare.return-001.mkv and the rings + of power-001.mkv.
Let's assume that we're in the first iteration and $f expands to nightmare.return-001.mkv

• ${f%-001.mkv} right-side-strips -001.mkv from $f; that would give ./source/nightmare.return. We store this prefix in the variable p.

• ${p##*/} left-side-strips all characters up to the last / from $p; that would give nightmare.return.

So ... -o ./joined/"${p##*/}".mkv "$p"-*.mkv would be equivalent to ... -o ./joined/nightmare.return.mkv ./source/nightmare.return-*.mkv

PS: Once you checked that the displayed commands correspond to what you expect then you can remove the echo