Change:
<ins> { config, lib, pkgs, ... }: let cfg = config.services.code-server; defaultUser = "code-server"; defaultGroup = defaultUser; in { options = { services.code-server = { enable = lib.mkEnableOption (lib.mdDoc "code-server"); package = lib.mkPackageOptionMD pkgs "code-server" { example = '' pkgs.vscode-with-extensions.override { vscode = pkgs.code-server; vscodeExtensions = with pkgs.vscode-extensions; [ bbenoist.nix dracula-theme.theme-dracula ]; } ''; }; extraPackages = lib.mkOption { default = [ ]; description = lib.mdDoc '' Additional packages to add to the code-server {env}`PATH`. ''; example = lib.literalExpression "[ pkgs.go ]"; type = lib.types.listOf lib.types.package; }; extraEnvironment = lib.mkOption { type = lib.types.attrsOf lib.types.str; description = lib.mdDoc '' Additional environment variables to pass to code-server. ''; default = { }; example = { PKG_CONFIG_PATH = "/run/current-system/sw/lib/pkgconfig"; }; }; extraArguments = lib.mkOption { default = [ ]; description = lib.mdDoc '' Additional arguments to pass to code-server. ''; example = lib.literalExpression ''[ "--log=info" ]''; type = lib.types.listOf lib.types.str; }; host = lib.mkOption { default = "localhost"; description = lib.mdDoc '' The host name or IP address the server should listen to. ''; type = lib.types.str; }; port = lib.mkOption { default = 4444; description = lib.mdDoc '' The port the server should listen to. ''; type = lib.types.port; }; auth = lib.mkOption { default = "password"; description = lib.mdDoc '' The type of authentication to use. ''; type = lib.types.enum [ "none" "password" ]; }; hashedPassword = lib.mkOption { default = ""; description = lib.mdDoc '' Create the password with: `echo -n 'thisismypassword' | npx argon2-cli -e`. ''; type = lib.types.str; }; user = lib.mkOption { default = defaultUser; example = "yourUser"; description = lib.mdDoc '' The user to run code-server as. By default, a user named `${defaultUser}` will be created. ''; type = lib.types.str; }; group = lib.mkOption { default = defaultGroup; example = "yourGroup"; description = lib.mdDoc '' The group to run code-server under. By default, a group named `${defaultGroup}` will be created. ''; type = lib.types.str; }; extraGroups = lib.mkOption { default = [ ]; description = lib.mdDoc '' An array of additional groups for the `${defaultUser}` user. ''; example = [ "docker" ]; type = lib.types.listOf lib.types.str; }; socket = lib.mkOption { default = null; example = "/run/code-server/socket"; description = lib.mdDoc '' Path to a socket (bind-addr will be ignored). ''; type = lib.types.nullOr lib.types.str; }; socketMode = lib.mkOption { default = null; description = lib.mdDoc '' File mode of the socket. ''; type = lib.types.nullOr lib.types.str; }; userDataDir = lib.mkOption { default = null; description = lib.mdDoc '' Path to the user data directory. ''; type = lib.types.nullOr lib.types.str; }; extensionsDir = lib.mkOption { default = null; description = lib.mdDoc '' Path to the extensions directory. ''; type = lib.types.nullOr lib.types.str; }; proxyDomain = lib.mkOption { default = null; example = "code-server.lan"; description = lib.mdDoc '' Domain used for proxying ports. ''; type = lib.types.nullOr lib.types.str; }; disableTelemetry = lib.mkOption { default = false; example = true; description = lib.mdDoc '' Disable telemetry. ''; type = lib.types.bool; }; disableUpdateCheck = lib.mkOption { default = false; example = true; description = lib.mdDoc '' Disable update check. Without this flag, code-server checks every 6 hours against the latest github release and then notifies you once every week that a new release is available. ''; type = lib.types.bool; }; disableFileDownloads = lib.mkOption { default = false; example = true; description = lib.mdDoc '' Disable file downloads from Code. ''; type = lib.types.bool; }; disableWorkspaceTrust = lib.mkOption { default = false; example = true; description = lib.mdDoc '' Disable Workspace Trust feature. ''; type = lib.types.bool; }; disableGettingStartedOverride = lib.mkOption { default = false; example = true; description = lib.mdDoc '' Disable the coder/coder override in the Help: Getting Started page. ''; type = lib.types.bool; }; }; }; config = lib.mkIf cfg.enable { systemd.services.code-server = { description = "Code server"; wantedBy = [ "multi-user.target" ]; after = [ "network-online.target" ]; path = cfg.extraPackages; environment = { HASHED_PASSWORD = cfg.hashedPassword; } // cfg.extraEnvironment; serviceConfig = { ExecStart = '' ${lib.getExe cfg.package}  --auth=${cfg.auth}  --bind-addr=${cfg.host}:${toString cfg.port}  '' + lib.optionalString (cfg.socket != null) '' --socket=${cfg.socket}  '' + lib.optionalString (cfg.userDataDir != null) '' --user-data-dir=${cfg.userDataDir}  '' + lib.optionalString (cfg.extensionsDir != null) '' --extensions-dir=${cfg.extensionsDir}  '' + lib.optionalString (cfg.disableTelemetry == true) '' --disable-telemetry  '' + lib.optionalString (cfg.disableUpdateCheck == true) '' --disable-update-check  '' + lib.optionalString (cfg.disableFileDownloads == true) '' --disable-file-downloads  '' + lib.optionalString (cfg.disableWorkspaceTrust == true) '' --disable-workspace-trust  '' + lib.optionalString (cfg.disableGettingStartedOverride == true) '' --disable-getting-started-override  '' + lib.escapeShellArgs cfg.extraArguments; ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID"; RuntimeDirectory = cfg.user; User = cfg.user; Group = cfg.group; Restart = "on-failure"; }; }; users.users."${cfg.user}" = lib.mkMerge [ (lib.mkIf (cfg.user == defaultUser) { isNormalUser = true; description = "code-server user"; inherit (cfg) group; }) { packages = cfg.extraPackages; inherit (cfg) extraGroups; } ]; users.groups."${defaultGroup}" = lib.mkIf (cfg.group == defaultGroup) { }; }; meta.maintainers = [ lib.maintainers.stackshadow ]; } </ins>

Discussion:
Currently, code-server (and openvscode-server) depends on 16 in nixpkgs, for the upcoming release of NixOS 23.11, this dependency must be dropped, and all upgrades must be performed to 18. From what I see on — 18 is supported as an engine. Otherwise, those programs are to be dropped. Please pick up the pieces cc
Drop will be performed in