Patient Gamers

Funny that you mention Life of Strange because it’s actually set in Autumn, but it does kinda have the vibes you describe. What does have way more summer vibes though is the prequel, Before the Storm, totally worth it if you’ve haven’t played it.

What Remains of Edith Finch, and The Unfinished Swan

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.

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. :)

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

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 :)

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.

"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

Try Stranded Sails. It's a tight little adventure game.

Brothers a Tale of Two Sons

Seasons After Fall

A Story About my Uncle

Subnautica

Raft

Ori 1 and 2 maybe

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

Here Comes Niko, "the cozy 3D platformer for tired people." You play an adorable sprite leaping around a tropical island chain. I don't think it has failure modes, in general.

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.