IN TYPO3 versions before 7.6 it was possible to render links inside the content element HTML
by using the TypoScript
tt_content.html.parseFunc.tags.
There are a couple of possible solutions for this question.
1.) Use fluid_styled_content.
I guess that now fluid_styled_content instead of css_styled_content is used. Therefore the used TypoScript does not work anymore. A valid solution would be to switch back to css_styled_content. However that is the old ancient way and for newer projects you shouldn't do this.
2.) Override the template of fluid_styled_content.
If you open the template of fluid_styled_content and the HTML element, found at typo3/sysext/fluid_styled_content/Resources/Private/Templates/Html.html
you will see
{data.bodytext}
this must be changed to
{data.bodytext}
Overriding is described in the docs, see https://docs.typo3.org/typo3cms/extensions/fluid_styled_content/7.6/Configuration/OverridingFluidTemplates/Index.html