I'm not an expert but from what I've seen Rust is one of the big alternatives. It's new enough to be trendy and fixed a lot of C++ issues whole being mature enough that the tooling is ok.
I'm also intrigued by Zig. I haven't used it for anything yet but the language looks fun and I believe platform.io supports it
Raspberry Pis are beefy enough that you could also get away with less systems-y languages. I like Kotlin. By default Kotlin needs a JVM but I think it's usable if you build native executables. However if you want to fiddle with GPIOs you might have to do it by manually setting things on/off in the filesystem (edit, sorry, just read you're using a PICO. Not sure how well Kotlin is supported)
The Pi Pico is a microcontroller, not a full linux-capable SBC. The confusion is helped by the fact that Raspberry Pi has a bunch of variants and almost all of them are SBCs.
I'm also intrigued by Zig. I haven't used it for anything yet but the language looks fun and I believe platform.io supports it
Raspberry Pis are beefy enough that you could also get away with less systems-y languages. I like Kotlin. By default Kotlin needs a JVM but I think it's usable if you build native executables. However if you want to fiddle with GPIOs you might have to do it by manually setting things on/off in the filesystem (edit, sorry, just read you're using a PICO. Not sure how well Kotlin is supported)