Is there a reason the string has to be put into the constructor, and the actual config happens at runtime?
It makes it difficult for DI and libraries/config to adjust the object ones in constructing and then using it.

If you look into e.g.
https://commonmark.thephpleague.com/1.5/extensions/github-flavored-markdown/
or https://github.com/kzykhys/Ciconia/blob/master/src/Ciconia/Ciconia.php#L42

Then you usually make the builder itself stateless and instead wrap statefulness internally.

$env = .. // Can contain all the filters and stuff
$options =  [
    'xhtmlOutput' => true,
    'strictMode' => false,
    'escapeHtml' => true
];

// We can pass defaults here if we want
$instance = new Decoda($env, $options);

// We can also set options here per convertion
$html = $instance->convert($bbcodeText, $options);
$html2 = $instance->convert($bbcodeText2, $otherOptions);

What do you think?

There will also be no need for reset() then as it keeps the wrapper stateless and reuses the objects here.