Started this morning and already overthinking everything — my results so far

That's a really good point and I should have said that in my OP. 10K is what worked for me but the message is really just "move more than you currently do." If you're at 2,000 steps, getting to 5,000 is a massive win.

I wish I could walk more but my knees are absolutely wrecked from carrying 130kg for 20 years. I can do about 4,000 steps before the pain becomes unbearable. Any alternatives that are similarly low-impact?

Absolutely! The goal is Zone 2 movement, not specifically walking. Options that are easier on joints:

• Swimming / water walking — zero impact, excellent cardio
• Recumbent bike — no weight on knees, can watch TV while riding
• Elliptical — low impact, mimics walking motion without the joint stress
• Chair exercises / seated workouts — YouTube has tons, no shame in starting here
• Upper body ergometer — arm cycling, usually available at gyms

Also — as you lose more weight on the GLP-1, the knee pain will likely improve and you may be able to increase walking gradually. Many of my patients experience this. Don't give up on walking forever, but don't force it through pain right now.

Listen to the advice above! And also — I had terrible knee pain at my starting weight too. Honestly, 25kg lighter and my knees feel like they belong to a different person. There's hope. ❤️