Patient Gamers

Maybe the Yo-Kai Watch games? They are RPGs probably inspired by Pokemon, but better in basically every way.

You play as a kid befriending Yo-Kai (creatures taken from japanese folklore), while exploring a pretty cool city. Has a nice soundtrack as well. The story of the first game is kinda meh, but I think it still has that summer vibe.

The second game is a lot better, with an actual story, more stuff to do and more to explore. Definitely the better game, but playing it first might make the first one less enjoyable afterwards.

Both of these games have that childhood summer adventure vibe, even though I myself didn't spent my childhood befriending Yo-Kai.

Likely in the ok-ish section but Celeste has that vibe going for it

I haven’t played it myself, but Boku no Natsuyasumi is a game that recently entered my radar, which fits your description quite well. It’s a game I want to play sometime, but I have had other priorities. It’s for PSX.

It’s about a boy in a summer vacation with his family.

Unfortunately there doesn’t seem to be any official English versions of the game, but hopefully you might find a solution if you think the game looks interesting enough to play it.

I'm not sure if it quite fits but the first game that came to mind was Minami Lane

Maybe the Atelier games would fit the bill? The recent entries, mostly the Ryza trilogy ("Atelier Ryza: Ever Darkness & The Secret Hideout", yeah, the title is a bit clunky) don't have the time limit that used to be a staple of the series. Instead, it is incredibly chill, a JRPG in a relaxed, colorful environment with an actually really fun, puzzle-like crafting system (called synthesis, their take on alchemy), which feeds masterfully into combat and resource collecting. It is very fun, and the game feels like going on a summer holiday with friends as a kid. :)

Surprised TOEM isn't on your list, given the premise is pretty much exactly what you describe. Last I checked it comes up on the first page or something if you sort steam by highest rated.

Lunacid might also be a good game. I think it fits your criteria for me, but that might just be for me.

The first thing that comes to my mind is Summer in Mara. It's a chill, relatively shallow farming sim with fetch quests and exploration.

Some more based on other games you liked:

• Arida - short-ish adventure game with a bigger emotional impact
• Nuts - probably most similar to Firewatch; core gameplay loop is taking pictures of squirrels, but there's some plot development
• A Juggler's Tale - side scroller adventure with some feels
• Deponia - funny point and click adventure series; if you like the genre, try The Darkside Detective (less "summer adventure" more "weird mysteries")
• Manifold Garden - more chill than The Talos Principle or The Witness, with less feels than the first; decent, trippy puzzle game

A lot of nice suggestions already, I'd like to add the Sorcery! games if you don't mind reading and enjoy exploring.
I personally really loved the world it portrayed and the tried so many different ways to finish the story.
Also, it has great maps, and I love maps :)

"What Remains of Edith Finch" could work. And "Man eater." What's more summer than a a shark?

Have you enjoyed any of the recommendations OP? I like your original list/taste and am wondering what else fit the aesthetic

Castle Crashers

Stanley parable ultra deluxe there was a bit in the desert so it fits.

The looker as you played the witness I really recommend this parody

E: +1 to a short hike

The Big Con

Toejam & Earl: Back in the Groove!

Alba: A Wildlife Adventure

It's perhaps a bit child-oriented, but is pretty fun, chill, and you can't do more "summer vacation" than that.

The Wreck