1. Freebies recommendations

-Workstations:
Ardour, LMMS, MPC Beats, CakeWalk, or openMPT/MilkyTracker if you like tracker music. VCV Rack 2 Free for modular synthesis. You can also evaluate a fully functional version of Reaper for two months, and the paid licence is cheap.

-Plug-ins - generators:
Kontakt Player, Reaktor Player, Synth1, Dexed, TyrellN6, Vital, Surge XT, BBC Symphony Orchestra, Steven Slate Drums Sampler, SINE Player + Berlin Free Orchestra

-Plug-ins - effects:
Guitar Rig Player, W1 Limiter, ReaEQ, OrilRiver, Valhalla Super Massive, Ozone 9 Elements, Fracture, Hysteresis, LoudMax, lkjb QRange, and everything by MeldaProduction, Chowdhury DSP and Tokyo Dawn (esp. TDR Nova)

-Samples:
Freesound, Ghosthack, Loopmasters, MusicRadar, Neurohop Forum, Prime Loops, Cymatics, Hyperbits, FreePats

2. Content recommendations

YouTube (mostly about composing/theory):
Anne-Kathrin Dern, Adam Neely, 8-Bit Music Theory, David Bruce Composer, 12tone, Signals Music Studio, Bill Hilton, Jeff Schneider, Nahre Sol, David Bennett Piano, Music Matters, Cadence Hira, Music with Myles, Walk That Bass, Implied Music, En blanc et noir, Tabletop Composer, Guy Michelmore

Reading:
-Your DAW's manual!
-Wikipedia and/or plug-in/hardware manuals for glossary such as parameters
-the "Synth Secrets" series on Sound on Sound for a deep dive into synthesis (someone on r/synthesizers compiled them into one pdf btw)

*Composing/western music theory (in this order):
-"Music Theory for Computer Musicians" by Michael Hewitt (or "Composing Digital Music for Dummies" by Russell Dean Vines)
-"Music Theory 101" (and the rest) by Tuberz McGee (or "Open Music Theory" by Hybrid Pedagogy Publishing) as a recap (alternatively, the "Learn music theory in half an hour." video by Andrew Huang)
-"Beyond Functional Harmony" by Wayne J. Naus and/or "Twentienth Century Harmony" by Vincent Persichetti
-bonus: en.xen.wiki, maqamworld.com, "Ancient Traditions - Future Possibilities" by Matthew Montfort, and Anuja K (YouTube again) if you're still interested in expanding even further

*Mixing/mastering:
-"Audio engineering advice" by Conor Dalton or "Mixing with iZotope" and "Mastering with Ozone" by iZotope (it does help even if you're not a mastering engineer and don't use iZotope's software), or "The Mixing Blueprint" and "The Mastering Blueprint" by Cymatics
-"Ultimate Guide To Compression" and "Vocal EQ Cheat Sheet" (helps with non-vocal stuff as well) also by Cymatics
-Mastering Explained and Frightbox Recording on YouTube
-"Mastering Audio: The Art and the Science" by Bob Katz if you need more after reading and watching the previous ones
-Sound On Sound articles if you feel like reading even more