If what really matters to you is GPS and reliability, Garmin deserves the reputation it has, but honestly you don't need to drop cash on the pricier models. With something like the Edge 130 Plus or the Edge 530 you've got more than enough for serious training: pretty accurate GPS, decent battery life, and syncing with platforms like Strava without any hassle. The 530 gives you a bigger screen and more features, but the 130 does the same thing in a more compact package.
If it still seems like a lot of money, Wahoo (like the Elemnt Bolt) is a solid alternative that runs similar prices or sometimes a bit less on some sites. Truth is, most cyclists I run into on training rides use Garmin, so you'll have a whole community and tutorials everywhere. Compass, altimeter, basic maps... everything you're asking for comes in these devices without going for the €500 pro versions.
My advice: check platforms like Amazon or bike shops to see where they're cheapest right now (prices drop quite a bit in September), and if you want something cheaper to start with, some phones with apps like Strava or Komoot track pretty well while you get the hang of it. But if you're serious about it, a basic Garmin will last you years.