“I believe the character you’re looking for is the Zero Width SPace with a character code of U+200B. This unprintable symbol is used in computerized typesetting to provide text-processing systems with word boundaries for scripts without specified spacing, ortoindicatethatalinebreakmayoccurafteracharacterthatisn'tfollowedbyavisiblespace.
Of course, the purpose you’d want here is to use it to separate 2 sets of 2 letters, like fuck.
You could also use the lowercase Cyrillic letter с, but most fonts this site supports don’t actually support Cyrillic characters.” - 🤓