For modded minecraft, you're looking at finding a good modpack. Modpacks are often built around a handful of mods (sometimes even a single mod can define the feel of a pack), but will invariably contains dozens or hundreds of mods. Just configuring everything to work together can be a major challenge; there's a similar amount of work and creativity that goes into curating a modpack as a mod.

As for what modpack, I'm not sure. I haven't played in a couple years and the scene moves fast, and plus, there's a lot of different types of packs. For example:

Some packs are tech focused, and expect you to start from sticks and mud and grind your way up the tech tree to create an enormous factory dedicated towards building a massive fusion reactor.

Others are magic focused, and instead want you to build elaborate alchemical labs, summoning circles, or similar.

Skyblock packs start you in a vast empty void, often on a single block of dirt, or a 3x3 block of stone, or on the branches of a single tree or similar, and expect you to build from there up to a "normal" endgame; generally there are special mechanics to help you do this (like being able to place barrels to collect water when it rains, or being able to sieve gravel looking for nuggets of ores), and often a quest system to reward you with key items by completing certain challenges. There's more work to do (you have to build the island from scratch, one block at a time, and there's always risk of falling off), but you have more control than if you just found a flat-ish plain and started building huts.

Some packs are "kitchen sink" packs that just have every mod the curator can find and get mostly working, focusing on changing the game as MUCH as possible.

Some packs are narrowly focused on a theme or mechanic, or have an actual story line. Crash Landing (https://ftbwiki.org/Crash_Landing) is a bit old now (but should still work fine!) and could EASILY have been a standalone game; it was a great story of trying to survive in a hellish desert after your ship crash landed and is one of my top 50 favourite games period really.

Some packs focus on making things hard. Their tech trees are aggressively deep, and your starting tools are sharply limited. These often contain GregTech (if tech focused).

Some packs focus on allowing creativity. Some mods let you create extremely elaborate base designs and decorations, or craft enormously powerful custom armor.

I'd recommend looking around the Feed The Beast (FTB) subreddit (https://www.reddit.com/r/feedthebeast/), installing the FTB launcher, trying out a couple recent packs, look at what packs people are chatting about, etc.

I haven't played any of these, but based on how things worked previously:

Direwolf20 1.12 Pack will be a middle of the road pack, and a popular streamer (Direwolf20) will have a very extensive lets play series of videos about it, so it's easy to get started.

FTB Stoneblock 2 is a reverse skyblock (you start in an infinite world of stone) with lots of quests and tweaks to make that work.

FTB Builders Paradise is more about building cool stuff than grinding out crazy tech trees.

FTB Continuum is just about grinding out crazy tech trees.

FTB Interactions is meant to BIG, well integrated, and since it has Gregtech, probably a bit slow.

There are many other packs (some of the most popular packs are NOT official FTB packs, but it's easier to find info on the current FTB packs), and many other launchers, and the above may not be right for you, but if you try a couple of those, and poke around the FTB subreddit, you should at least get a feel for what direction you'd like to go in.

Also, I highly recommend finding lets plays to watch at first; modded minecraft can be hard to get into because it's basically a series of new games, built out of mods, built on top of a hacked API, built on top of a sandbox game; there's a LOT of layers to the onion, and not a lot of documentation. :) Stuff like learning how to use JEI to quickly lookup items and how to craft them is critical when trying to understand a new modpack that might literally add thousands of items and recipes.