grotty is capable of ECMA-48:1976 and ISO 8613-6:1994 control sequences, and can actually do proper italicization, boldface, underline, and colour in manual pages; which many terminals nowadays have supported for decades.
* https://jdebp.eu/Softwares/nosh/italics-in-manuals.html
mandoc still only knows the old 1960s TTY-37 control sequences that use overstrike for boldface and underline and that have no notion of italicization or colour.
When FreeBSD switched from groff to mandoc, I went looking for any way to have mandoc support ECMA-48:1976 and ISO 8613-6:1994 control sequences. It turned out to be a large amount of work to bring it up to parity with something that the GNU toolchain has had since the 1990s (and is in fact the GNU toolchain's native mode of operation).