You could use the find command with a -regex test

$ find /path/to/folder -regextype posix-basic -regex '.*/.{5,}'

or

$ find /path/to/folder -regextype posix-extended -regex '.*/.{5,}'

Note that -regex is a path match rather than a file match - hence you need to match the leading .*/ as well, before the 5+ character filename

Alternatively, for a pure bash solution, you could enable extended shell globbing and then use the pattern !(@(?|??|???|????)) meaning 'anything that does not match one or two or three or four characters'

$ shopt -s extglob

$ ls -d /path/to/folder/!(@(?|??|???|????))

If you want to include subdirectories, you can enable the globstar option as well and add a ** wildcard i.e.

$ shopt -s extglob globstar

$ ls -d /path/to/folder/**/!(@(?|??|???|????))

for example

$ ls -d **/!(@(?|??|???|????))

abcde  abcdef  abcdefg  subdir  subdir/abcde  subdir/abcdef  subdir/abcdefg

while the non inverted matches (files shorter than 5 characters) are

$ ls -d **/@(?|??|???|????)

a  ab  abc  abcd  subdir/a  subdir/ab  subdir/abc  subdir/abcd

To unset the options afterwards, use

$ shopt -u extglob globstar