MC has an evil/different side he only shows ML System Novel where MC doesn't get together with the 'main target' of his mission, rather he gets together with either a sidecharacter/passerby/villain/ogloveinterest or the system. Also, no useless & annoying systems if its the former. MC that went back in time and is healing x ML who supports him. Revenge novel where MC &/ ML actually encounters some difficulties along the way. Preferably something where they explain the reason for his revenge or details of his tragic past early on or gradually during the story. One where I can actually hate the antagonists not like the one I just dropped, I mean, could you rlly blame him for breaking up to avoid getting caught up in black material? The guy didn't even instigate it, he didn't even cheat or anything, he even let him get some resource and boost from his own popularity before the incident, what do you want me to do? Hate him for doing something logical???
I just read a few chapters of a BL QT (fairly short, about 91 chapters only) this morning and it ticked I think 1 and 2 of what you're looking for, mainly 2 lmao The Green Tea is Always Targeting the Wrong Person! I didn't actually even finish the first arc because it wasn't my cup of tea, but almost all of its reviews are good! But from the few chapters I read, the MC is super cool and the part where you're unsure about who he's going to get together with as you can infer from the title.
After the Bankruptcy of the Supporting Male Lead - 2(MC transmigated after the end of the story) I'm the Vicious Canon Fodder in the Book - 3 & 4(sort of, since ML is fighting for the throne) Mistakenly Saving the Villain - 2(you've probably read this already)