For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
// Add JavaScript Frameworks
JHtml::_('bootstrap.framework');
// Load optional RTL Bootstrap CSS
JHtml::_('bootstrap.loadCss');
There's a 'bootstrap tabs' template which (once you have your template loading bootstrap) achieves this.including tabs in the form edit.