groff can produce output with links in it, and does by default in HTML mode! The GNU version of the Unix man page macro set has .UR and .UE for “URI start” and “URI end”. (I don't know whether these were present earlier in the lineage or whether they were introduced by GNU.) Also, the lowdown Markdown converter when in man output mode will output those for links. For fun, try:

    echo 'Hi there! Have a [hyperlink](https://www.gnu.org/software/groff/manual/groff.html).' | lowdown -st man | groff -man -Thtml

There's also support for OSC 8 terminal hyperlink sequences throughout most of the groff toolchain: grotty(1) supports outputting them, and less(1) supports passing them through, including ^O^P and ^O^N gestures for moving between them. But man(7) says they're not enabled for grotty output by default. “Options” describes the rationale in its item for “-rU1”: “grohtml enables them by default; grotty does not, pending more widespread pager support for OSC 8 escape sequences.”

So if I set MANROFFOPT=-rU1 in the environment, I can get clickable links in man… if the man page author included them that way in the first place. I'm not sure how common that is in the wild, but grepping the ones on my system, I find firejail(1) contains a link to a GitHub issue embedded in that way, and it does indeed work when I hit ^O^N to seek to it and then C-mouse1—though the mouse gesture I have Alacritty using for links doesn't seem to work through tmux (there might be a way involving twiddling the tmux terminal-features setting, but I ran out of steam before trying this), and I didn't see a great way to get either grotty or Alacritty to style them on display instead of having them blend into the surrounding text, so it's still kind of scuffed in practice. (Though I bet the cool kids have moved on from Alacritty by now?) less displays the link target in the status line when you use the navigation commands, so it's not inaccessible, but for opening selected links directly from less with the ^O^O gesture rather than leaning on terminal support, it looks like you need to explicitly set the LESS_OSC8_ANY and/or LESS_OSC8_‹scheme› environment variable to a shell command that outputs a shell command pattern to substitute the link into; if I set LESS_OSC8_ANY='echo xdg-open %o' then it passes it to my Firefox. I wonder if they'd take a patch (or if any existing distributions patch it) to use that as the default?

That was a fun little rabbit hole to go down, thank you.