Since TYPO3 8.7.x it seems that:
lib.parseFunc.tags.link.typolink.ATagParams =style="style="color:#000; text-decoration:underline;font-size:16px;"
dosen't exist no more in fluid styled content. Works in 7.6. Also
lib.parseFunc.tags.a.typolink.ATagParams.data = style="color:#000; text-decoration:underline;font-size:16px;"
retained in frontend.
Related issue but marked as solved: forge.typo3.org
Yes, lib.parseFunc.tags.link does not work anymore since the "link"-tag for RTE placed internal links has been replaced by normal <a href="t3://anything"> links.
Your possible mistake is that you want to change the ATagParams statically. .data is expecting some data to read from. You need to empty the .data function first because it takes precedence. Then you can set the ATagParams statically.
Please try it like this:
lib.parseFunc.tags.a.typolink.ATagParams.data >
lib.parseFunc.tags.a.typolink.ATagParams = style="color:#000; text-decoration:underline;font-size:16px;"
Please note that this will affect all links!