I setup Zeus and connected it to my alby. I tried to zap and the default was 1000 sats and I couldn’t change it. I’ll have to look into it some more I guess.
You can use your existing Alby wallet on mobile by linking it to the #[2] app. If you want something separate, then #[3] or https://LN.tips are good too.
Discussion
Which Nostr app are you using? You can change the default zap amount in the app settings. In Damus, for instance, it’s under Settings > Zaps.