I think a lot of people get intimidated to learn a new RPG because they think it's always going to be as intense as learning DnD.
DnD is a lot. There are other RPGs that can fit in a png.
This is 100% of the game. Every piece of published material is right here. It is also entirely free. If you do not have time to try other, bigger RPGs, but you have the general grasp of how the flow of play works (DM describes a thing, you respond in character, etc.), then Start Here.
Scrolls & Swords is going to fit very well with the same kind of classic fantasy settings that you see in DnD, but it's going to be much more flexible to your group. If you really like homebrewing DnD (which it sounds like you do), Scrolls & Swords is robust yet small enough to be an excellent starting point for that. It lends itself well to Rule of Cool styles of play, but also a focus on common sense play ("Of course you know how to saddle a horse, you used to be a stablehand," and so on), depending on which your group leans into more. Additionally, these rules don't just apply to combat, but anything your DM decides would be an interesting challenge. That means you use exactly the same rules for combat as you do for seducing a guard or haggling a better price or riding in a horse race.
If you decide to download that image, you now own a copy of a full RPG system to the fullest extent that you can own anything and can then use it to run your next campaign.
Learning DnD can be an expensive and genuinely massive undertaking, especially if it's your first RPG (which it sounds like it is). What a lot of people don't realize is that most RPGs aren't like that. The majority of them are going to be a single novel sized book for half the price of one DnD book. And I mean that novel is everything: rules, character stuff, GM reference, and even a few starting adventures, for less than the price of the Player's Handbook.
The thing is, if you currently have time to play DnD, you have the chance to pause it for two sessions and spend that time reading a new game. Keep in mind, if you do pick a novel-sized game, that includes everything that the three core books of DnD covers, so you will not even need to read the whole book (your GM will, or will at least need to read a bit more than other folks in your group). I know that DnD is huge, but the majority of these other games simply are not that; you really can get everything in the same time as two DnD sessions.
I'll list some that I really like, and I'll make sure to only include shorter rulebooks with a low-ish price point.
Mouse Guard
Play as a little mouse protecting an entire frontier of mice! It uses the Burning Wheel system, which means you're going to still be defining your characters' skills very clearly, but you do so by outlining their life experience and family. Very clear about the roles of the GM and the players, so it's hard to feel "railroaded" or lost.
Monster of the Week
If Buffy, The Dresden Files, or Supernatural were an RPG. Uses Powered by the Apocalypse, so you'll still have a "class" but it's really going to fill out your narrative role and relationship to other characters really well (like if you rolled your background, class, and character bonds and flaws into one neat package). It's going to be good if you don't like the grid combat of DnD and wish it focused on the drama of a fight more, or if interacting with NPCs or solving mysteries is your favourite thing to do in a game.
Crash Pandas
Play as a band of raccoons in an illegal street race, all trying to drive the car at the same time. Made by the same person who did Honey Heist (which I also recommend), so you can expect the same kind of goofy, easy-to-learn style. It's another one-page game like Scrolls & Swords up there (albeit a bigger page) and is equally free. You can own it for $0 and a quick google search if you wanted.
I hope these can get you started. DnD is massive so if it's the first RPG you've played, it can make all RPGs seem equally daunting. If you take nothing else from this, know that other RPGs are far more accessible than DnD might make them seem.