Ask HN: What language/stack to use for “customer ready” SBCs/sensors/GUI?

I've been making various systems using RPi/Arduino/ESP8266 and sensors for a while, but very hobby level. Adafruit parts, prototyped using breadboards, copy/paste code from online and modify it. Have made a few weather stations, and basic home automation.

I'm completely in love with this, and want to take it further, and do these projects "properly".

I don't know any "real" programming languages, but have been tinkering with web projects for 30+ years (php, mysql, js, css, cgi/perl back in the day). Just for background. So I'm willing to learn anything required from scratch, and timeframe doesn't matter, I'm willing to commit long term.

What absolutely matters, is I want to learn stuff that will still be around years from now. I don't care about the latest/greatest frameworks/languages, but longevity and reliability are paramount. These projects will end up being used in real-life situations on family farms and in family companies, and I want them to be good enough to set/forget.

Getting sensor data read and stored is easy enough in any language, but I'd really also like to be able to put nice GUIs on touchscreens for it. I currently do that with Raspbian + i3wm and web apps, which has ridiculous overhead. I'd like the final products to be on-par quality-wise with in-car headunits and other commercially available touch interfaces.

Python + Qt/PyQT? Python + Kivy? Something entirely different?

Any suggestions on stacks/pathways for this are appreciated.