"fold" includes the character '\e' and each of the following characters that are used to format text as if they were all visible.

Example:

echo "a\e[3mb\e[0mc" | fold -w1

Result:

a

b

c

It still formats correctly, it just breaks too early.

Special characters can even be broken up.

Example:

echo "君の名は" | fold -w1

Result:

�
�
�
�
�
�
�
�
�
�
�
�

In case this appears invisible or otherwise different: It's 12 lines with one "tofu"/U+FFFD/replacement character each.

I would maybe expect issues like this when the "-b" option is given, since that counts bytes, but it happens even without it.

While trying to work around this, I noticed a similar issue with "wc":

echo -e "\e[3ma\e[0m" | wc -cm
10 10

I have not investigated this further so far.