when using doublequotes or interpolated regexes one needs to escape a leading backslash, hence "\\0"

your code is not replacing the string '\0' but the chr(0)

  DB<13> x "\0"
0  "\c@"
  DB<14> x chr(0)
0  "\c@"
  DB<15> x '\0' # with singlequotes escaping is only needed for \ and 
+'
0  '\\0'
  DB<16> p '\0' eq '\\0'
1
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