Bitcoin cli asks to use estimatesmartfee with new syntax that is not described in docs In previous versions of bitcoin-cli I've successfully used estimatesmartfee 2 syntax. But now cli answers {'errors': ['Insufficient data or no feerate found'], 'blocks': 0}. How should I estimate fee now?
estimatesmartfee requires that bitcoind have been running long enough to gather data about the current fee rates on the network. This can take some time. Try running it again after a few hours, or a day or so, once it has collected data.