The real juice of modded minecraft is in the modpacks - curated sets of mods that were configured to work well with each other, frequently with some custom recipes added by the pack developer, and sometimes some kind of a quest line to guide you through the pack and provide a more structured experience. There are many different types of modpacks - kitchen sinks (large collections of mods, frequently without a lot of balance tweaks or changes, for a more sandbox experience), questing packs (with the aforementioned quest books to guide you through the mods), vanilla+ packs that intend to expand on the vanilla minecraft experience and not change the gameplay loop significantly, packs focused exclusively on magic or technology mods (or both), expert packs (questing packs with heavily reworked recipes, where you need to build elaborate machines and automate stuff Factorio-style)...

I'm not up to date with the modpack scene, so can't really make you a definitive list - back on reddit (sigh) there is a r/feedthebeast community that specializes in modded play.

That said:

• FTB Academy seems to be a pack specifically meant to teach the basics of modded play.
• Project Ozone 3 comes up quite often as a pack with a good quest book that guides you through everything.
• Cottage Witch is what I'm currently starting, it's (so far) a chill magic vanilla+ pack. New creatures, new plants, some new mechanics, tons of new decorations for building.
• Peace of Mind is an older pack made specifically for playing on Peaceful, if mobs are stressing you out. It's got a good questbook too.
• and if you want to jump straight into the deep end... Enigmatica 2 (or 6) Expert, Gregtech New Horizons. Expert packs in which you need to automate everything to progress. Gregtech in particular is infamous for its complexity, difficulty, and length, but if you enjoy solving hard problems it might be for you.

You'll also need a launcher to install these packs - FTB have their own if you want FTB Academy, otherwise there are some options such as Curseforge (do not recommend, eats resources just by existing), Prism (seems to come up a lot as a recommendation), or GDLauncher (what I'm using).