As for games, I admit I haven't tried many of them but the Explorable Explanations I have tried are great, particularly the ones by Nicky Case (Parable of the Polygons , the Evolution of Trust , the Wisdom and/or Madness of Crowds). I'd call these short games even though they lean strongly towards elements of education and simulation.

Doing any nature related activities away from screens, whether it be daily walks, gardening, hiking, kayaking, mountain climbing, swimming, camping is really good for both mental and physical health.

In that blue zones documentary, it's said that daily walks and daily gardening help your mind and longevity more than any other activity.

Learning a musical instrument is always good, and is something you can show off. Knitting, crocheting, or any kind of ravelry works your mind, and you can also listen to audiobooks while doing it. Woodworking (you can start small, even doing spoons and things).

I wouldn't be too focused on doing mentally challenging activities. Screens wear out our brains enough, and what we really need is time away from them to recharge.

Outside of that I'd just recommend reading a lot of non-fiction, audiobooks where available.

Get into Ham Radio, not just get a license and talk, get into it. make your own radio, antennas, learn the science, learn firmware programming and microcontrollers, everywhere you turn there is something new to learn and puzzle at. And you can help with community service things (only if you want to). It’s great because you can go as deep as you want (or as shallow), keep your mind engaged and have fun doing it.

Books on early christianity (first two-hundred years) have been super engaging for the past 20 months. I'm an atheist, so this was a surprising topic to be of such interest.

For mainstream opinions, Bart Ehrman has a bunch of books. "How Jesus Became God," was especially good, as Jesus only preached that he was the Mesiah.

For stuff that's a bit edgier, there's the theory that Jesus was an ahistorical figure (three books into that topic and I believe this to be true), you could try Robert M. Price or Earl Doherty.

You could also check out random wikipedia articles. Plus podcasts:

Noble Blood focuses on historical events through the lenses of nobility (I’m a history nerd).

Stuff the British Stole is a seasonal show that deep-dives stolen museum items and their legacy.

(Are you detecting a trend?)

The Fall of Civilizations podcast deep-dives ancient civilizations. Phenomenal.

(Spoiler: I'm a history nerd.)

History of Rome is a long series of short episodes from a historian. It’s very amateur at the beginning.

(There it is again!)

What did you used to find stimulating?

Maybe learn programming, or other language.

https://www.philosophizethis.org/podcast

The gift that keeps on giving.

Wikipedia for sure

I personally love reading articles on Red Sails and ProleWiki. There's always more to learn about Marxism-Leninism, and these sites are treasure troves.

I also like meditation to clear my head.

WikiTok Bloomscroll through Wikipedia articles

Simon Tatham Puzzles Micro games

yucata.de Online boardgames

librivox.org Free audio-books

I am in the same boat. Currently forcing myself to get into D&D even though I’m completely shit at math, creative writing, art, and am not fantasy genre savvy. I want to create a homebrew game for my spouse that they’ll (hopefully) enjoy. It’s been really challenging so far but also a lot of fun.

Philosophy is excellent food for thought, working through a MOOC course (MIT/Yale?) and doing the prescribed readings might strike your fancy. Happy to give more specific recs if you have some existing curiosity about a topic. Side note that it’s difficult to find people to talk to online about serious philosophical topics, the options I’ve seen (discord groups, facebook groups) usually aren’t very engaging but the reading and lectures and contemplation are engaging on your own imo.

Watch ancient history documentaries like the Fall of Civilizations or History with Cy channels on youtube (Fall of Civilizations is also/originally a podcast if you prefer). Whenever I am feeling empty of interesting thoughts this is my go to. When I watch frequently I constantly find my thoughts combining and recombining history with my current experience in a way that feels awfully close to intellectual stimulation. I also find it gives some mildly comforting perspective on current events.

Built to purpose gadgets. Getting into arduino or similar as a hobbyist can be intellectually engaging. The process of identifying something in your space you could enhance then drafting and executing a plan (including some basic programming) is kind of like a puzzle. Building things you don’t need like an LED based checklist for chores that resets every day, a pedestal that spins to give a house plant even sunlight, or a solar powered bird house might be a fun challenge.

Edit to add that if you live near a university professors will usually let you unofficially audit their class if you’re interested in a topic and have time during the week.

There's a near-endless supply of great mythology and legend to read and explore from all sorts of cultures dating back as far as the dawn of writing. I've had a lot of fun reading and comparing tales from various times and places, taking time to also note where in history the stories were being written down and what else was happening. Strong recommendation for anyone wanting a unique view on the history of societies and the stories they held (or still hold) dear.

There is a pretty interesting rabbithole of semiconductor industry blogs (seminanalysis, chips and cheese, fundamental bottom) that can be fairly interesting to stay up to date on current hardware developments even without an CE/EE background.

I liked the human resource machine games. I’m currently reading Foucault as well I find it pretty stimulating even if I think he could have used simpler language to get his point across clearer.

So... I feel like I waste most of my time, but the things I can think of are philosophy and science videos, books, music theory and practice. The problem is consistency for me. Perhaps a group, a class, a club, or something like that if you struggle with it too.

I like books about history, and independently released books about any topic.