Decrease gap limit to 21

[MaxHillebrand]

We increased the gap limit because of some synchronization problems in the past, these are fixed now, and a larger value leads to longer loading time.

We should decrease the gal limit to 21.

[turbolay]

Reply by @lontivero on a PR I made in the past: #10473 (comment)

If consensus changed I can reopen it

[GeetaCX]

21 might be too low when promoting privacy preserving habits like never giving the same address to two entities.

Some wallet like Green wallet will display a new address everytime one go back and forth the receive page, some will constantly show the last one until coins are received, two extremes. wasabi and electrum seems to be in the middle with manual creation of new addresses, Wasabi is forcing the use of labels which leads people to create fake label name and clicking on any at random one to just get past that step.

A gap limit of 50 should cover the vast majority of edge cases.

[collins-okafor]

Would like to work on this

[kristapsk]

Small gap limits cause problems in some use cases, for example, when you use wallet in Wasabi, combined with same wallet as watch only (xpub) in BTCPay Server or SatSale. Which seems normal practice for merchants to me, you might not want to expose hot wallet to a server online. I have this problem with https://donate.kristapsk.lv and Blue Wallet currently.

[turbolay]

Still no consensus, closing. Better keep as it is.