`banlist.dat` was introduced in https://github.com/bitcoin/bitcoin/pull/6310, storing nodes that were automatically banned (due to exceeding the misbehavior threshold) and manually banned (through the `setban` RPC).

Automatic bans were removed in https://github.com/bitcoin/bitcoin/pull/19219 and replaced with a discouragement filter. That filter is not saved to disk/persisted over shutdown/startup. The `banlist.dat` therefore now only contains addresses that have been banned through the `setban` rpc.

Since https://github.com/bitcoin/bitcoin/pull/15935, we have a specific file for configuration that is updated through the RPC and persisted over shutdown/startup, namely `settings.json`. We should therefore move the manual ban configuration from `banlist.dat` to `settings.json`. Doing so has a couple of benefits:

- `settings.json` is human readable and easily analyzable by any json parser.
- we wouldn't need to maintain custom [de]serialization code for the `banlist.dat` file.

`banlist.dat` is expected to be fairly small and infrequently updated, so disk space/performance are not huge concerns.
strLoadError = _("Error initializing block database");
                    break;
                }
                 
                 
                bool failed_chainstate_init = false;
                for (CChainState* chainstate : chainman.GetAll()) {
                    chainstate->InitCoinsDB(
                        /* CoinDBCache,
                        /* alse,
                        /* Reset || fReindexChainState);
                    chainstate->CoinsErrorCatcher().AddReadErrCallback([]() {
                        uiInterface.ThreadSafeMessageBox(
                            _("Error reading from database, shutting down."),
                            "", CClientUIInterface::MSG_ERROR);
                    });
                     
                     
                    if (!chainstate->CoinsDB().Upgrade()) {
                        strLoadError = _("Error upgrading chainstate database");
                        failed_chainstate_init = true;
                        break;
                    }
                     
                    if (!chainstate->ReplayBlocks(chainparams)) {
                        strLoadError = _("Unable to replay blocks. You will need to rebuild the database using -reindex-chainstate.");
                        failed_chainstate_init = true;
                        break;
                    }