> So you kind of need familiarity with the genre to understand some of the jokes.
>> what are some tropes which are specific to dating sims rather than those also found in romance-based anime/manga?
It's been a while since I've read DDLC but familiarity was probably too strong a word. Having expectations about how the story should develop and then having those subverted is a good chunk of the fun [1]. So skimming at least one dating sim vn is probably enough context. And anime / manga also cover most of that context / japan-isms that DDLC mocks (eg the school setting, the childhood friend / council prez / spoiled imouto archetypes).
To your question though, the VN-specific jokes are mostly about the route system and world building. I guess these still fall under the umbrella of "bad endings" and "save then go back" but imo it's a huge umbrella that's worth exploring.
So like you mentioned, DDLC toys a lot with the concept of multiple routes / save files. In most VNs each route starts the same story before branching. You don't normally expect this "common route" to change between tries but in DDLC it does in multiple ways. But more uniquely, DDLC also questions why these romantic endings exist in the first place and arrives at the conclusion that the romantic interests are psychotically obsessed... by the design of some god [2]. This also pokes at how some VNs just rewrite the world between routes to avoid distractions from the chosen love interest, as in big events that are inevitable in one route just don't happen in others.
I also thought the choice system (the poems) in itself was a fun joke. Like most VNs have screens that let you vote on which route to read, one choice per route. After N screens you get placed on the route you picked most. DDLC exaggerates this by giving you 100s of screens each with multiple choices per love interest. Kind of like "Are you really really sure? Is this your final answer?"
Speaking of DDLC, I should really reread Totono [3]. It's another VN-parody but less gimmicky and a bit more serious / emotional.
[1] https://github.com/Bronya-Rand/DDLCModTemplate2.0/blob/v1.1....
[2] https://github.com/Bronya-Rand/DDLCModTemplate2.0/blob/69aa2...
https://github.com/Bronya-Rand/DDLCModTemplate2.0/blob/v1.1....
[3] https://store.steampowered.com/app/1293820/YOU_and_ME_and_HE...