No i have a good pc and a good Internet with ethernet cable many spanish people said the same thing that cubecraft has lag and is not optimized
That's anecdotal evidence and isn't what most of us experience generally.
I've got a PC that's optimised for Minecraft and ONLY Minecraft, doesn't run anything else (especially) in the background, on decent gigabit ethernet using decent routers and a great internet connection that isn't being used a ton for Netflix or other bandwidth heavy stuff... my ping to cube EU is often really low at around 11ms or usually under 60ms for the actual servers the games run on... I almost NEVER get identifiable lag from the server except on some of the buggy games such as Egg Duels (where the servers very regularly restart and the games can be unusably laggy).. but those are not normal for the main game modes which are in my experience almost always decent. Ensure your PC can actually handle the resolution and framerates you are trying to run your game at.. watch youtube videos on how to optimise PCs and GPUs etc for gaming.
Put another way... I'd hazard a guess that 90% of the lag (if not more) that players experience is due to something BETWEEN them and Cubecraft and not attributable to Cubecraft servers. eg.. you think you have a good PC but are you running awful AV programs like Norton on them or do you have a ton of other stuff open and running in the background. Do you regularly restart Minecraft (it gets laggy the more it's left open and needs restarting daily at least for 1.19 (bedrock) I've found. Older versions were somewhat better but still needed restarting after a while.
Do you
KNOW your local network is good.. are you sure your Ethernet is running at full capacity... It's always amazing how many people plug ethernet cables in and just assume they are working properly.. only to find it negotiated 10Mbps half duplex. Make sure you're running at full duplex at the speed your switch/router runs at (either 100Mbps or Gigabit usually). Half duplex is an utter killer for most things including online gaming. In Powershell run this...
Get-NetAdapter | SELECT name, LinkSpeed, fullduplex | ft -autosize
..oh and always prefer Ethernet over Wifi.. Wifi is a killer for gaming unless you have really decent Wifi and aren't in congested Wifi areas. Ethernet is the way to go.
Do you
KNOW your local internet connection is running well.. or are other family members chewing up bandwidth and resources. It's amazing how many people have a great connection which then degrades badly once some family members are streaming Netflix/YT etc at the same time.
Are you
sure you have a decent router for gaming? Many ISPs (especially at the cheap end or those that have millions of customers) buy awful routers for their customers and then fail to configure them optimally. It's not easy to know how to buy a decent router or how to configure them well.. but be aware that really poor routers that are configured badly can have a huge impact especially on gaming. It's worth taking the time to learn if you really want optimal setups for gaming.
Are you
sure you have decent internet? Have you taken the steps necessary to
KNOW that you have or are you just using anecdotal evidence like.. "well it works ok for xyz". In a command prompt run..
ping play.cubecraft.net -t
and leave it running for a long while.. maybe a day or so, then press CTRL C and see what your average stats were and how much packet loss there was. Packet loss should always be under 1%. It it's more then you need to investigate further as to why.. try pinging google or other well known services using the -t option and leave running. If they're all showing packet loss.. the problem is your or your ISPs network, not Cubecraft.
Then consider that play.cubecraft.net isn't likely the actual server you're connecting to it's cube's main IP, but not the IP of the servers the games run on. It's buggy, but run the ping command
in game to get a better idea of your RTT (round trip time / ping) to the actual game server. Also run a traceroute (tracert play.cubecraft.net on Windows) to see where any congestion is between your ISP and Cubecraft.. though I realise that that's not always easy to understand / interpret, but not too hard to learn about.
Also consider that lots of ISPs throttle internet connections and it's usually done in such a way that there is almost no way you could prove this. Buy internet from a decent reputable provider that people know and trust. As a rule of thumb, the general old Telephone companies in each country like BT, Virgin Media, Telefonica, Deutsche Telekom etc are generally not good. Smaller companies that actually care about their customers are the better ones to use (generally).
TLDR: Only run Minecraft on your PC. Switch off bad AV software and other background stuff that not needed. Prefer Ethernet over Wifi. Ensure you have a decent Full Duplex connection. Ban your family from streaming while you are playing. Buy internet and routers from decent / trusted suppliers.
HTH