You've got to disassemble the boiler and remove the scale from there. I run a Gaggia Classic at home with really hard water and my machine literally stopped flowing due to scale buildup. Once I fully pulled it apart and scraped all the scale out of the inside of the boiler it started running flawlessly.

https://greatinfusions.com/blog/great-infusions-coffee-blog/...

Would sound absurd to all but the nerdiest, most dedicated, but have you considered making your own water[0]?

[0] https://www.baristahustle.com/diy-water-recipes-the-world-in...

Or just buy bottled water. If you're only doing Espressi, a 1 liter bottle can take you a long way and comes in under 1 Euro.

For a daily thing like coffee I gotta set myself up for the most sustainable path or it feels like I'm accepting the waste

Very neat!

Exact same thing happened to me, I sold the Gaggia and now I'm considering getting a manual one. The only issue is hot water as well as needing a separate steam wand, I wish there was an all in one solution for that.