I bought a small Ubuntu server myself and gave me this error at startup, as reported below
Starting org.bukkit.craftbukkit.Main
System Info: Java 19 (OpenJDK 64-Bit Server VM 19.0.1+10-Ubuntu-1ubuntu122.04) Host: Linux 5.15.0-56-generic (s390x)
Loading libraries, please wait...
[05:31:33 INFO]: Building unoptimized datafixer
[05:31:34 INFO]: Environment: authHost='https://authserver.mojang.com', accountsHost='https://api.mojang.com', sessionHost='https://sessionserver.mojang.com', servicesHost='https://api.minecraftservices.com', name='PROD'
[05:31:34 INFO]: Found new data pack file/bukkit, loading it automatically
[05:31:35 INFO]: Loaded 7 recipes
[05:31:39 INFO]: [STDERR]: java.awt.AWTError: Can't connect to X11 window server using 'localhost:10.0' as the value of the DISPLAY variable.
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment$1.run(X11GraphicsEnvironment.java:105)
[05:31:39 INFO]: [STDERR]: at java.base/java.security.AccessController.doPrivileged(AccessController.java:318)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment.initStatic(X11GraphicsEnvironment.java:64)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment.<clinit>(X11GraphicsEnvironment.java:59)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.PlatformGraphicsInfo.createGE(PlatformGraphicsInfo.java:37)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.GraphicsEnvironment$LocalGE.createGE(GraphicsEnvironment.java:93)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.GraphicsEnvironment$LocalGE.<clinit>(GraphicsEnvironment.java:84)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:106)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11.XToolkit.<clinit>(XToolkit.java:224)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.PlatformGraphicsInfo.createToolkit(PlatformGraphicsInfo.java:41)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.Toolkit.getDefaultToolkit(Toolkit.java:595)
[05:31:39 INFO]: [STDERR]: at java.desktop/javax.swing.UIManager.getSystemLookAndFeelClassName(UIManager.java:667)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.gui.ServerGUI.a(ServerGUI.java:49)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.dedicated.DedicatedServer.bi(DedicatedServer.java:543)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.Main.lambda$main$2(Main.java:299)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:326)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.Main.main(Main.java:286)
[05:31:39 INFO]: [STDERR]: at org.bukkit.craftbukkit.Main.main(Main.java:302)
[05:31:39 INFO]: [STDERR]: at io.papermc.paperclip.Paperclip.lambda$main$0(Paperclip.java:42)
[05:31:39 INFO]: [STDERR]: at java.base/java.lang.Thread.run(Thread.java:1589)
[05:31:40 INFO]: Stopping main thread (Ignore any thread death message you see! - DO NOT REPORT THREAD DEATH TO PAPER)
[05:31:40 INFO]: Stopping server
[05:31:40 INFO]: Saving worlds
[05:31:40 INFO]: ThreadedAnvilChunkStorage: All dimensions are saved
[05:31:40 INFO]: Flushing Chunk IO
Starting org.bukkit.craftbukkit.Main
System Info: Java 19 (OpenJDK 64-Bit Server VM 19.0.1+10-Ubuntu-1ubuntu122.04) Host: Linux 5.15.0-56-generic (s390x)
Loading libraries, please wait...
[05:31:33 INFO]: Building unoptimized datafixer
[05:31:34 INFO]: Environment: authHost='https://authserver.mojang.com', accountsHost='https://api.mojang.com', sessionHost='https://sessionserver.mojang.com', servicesHost='https://api.minecraftservices.com', name='PROD'
[05:31:34 INFO]: Found new data pack file/bukkit, loading it automatically
[05:31:35 INFO]: Loaded 7 recipes
[05:31:39 INFO]: [STDERR]: java.awt.AWTError: Can't connect to X11 window server using 'localhost:10.0' as the value of the DISPLAY variable.
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment$1.run(X11GraphicsEnvironment.java:105)
[05:31:39 INFO]: [STDERR]: at java.base/java.security.AccessController.doPrivileged(AccessController.java:318)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment.initStatic(X11GraphicsEnvironment.java:64)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11GraphicsEnvironment.<clinit>(X11GraphicsEnvironment.java:59)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.PlatformGraphicsInfo.createGE(PlatformGraphicsInfo.java:37)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.GraphicsEnvironment$LocalGE.createGE(GraphicsEnvironment.java:93)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.GraphicsEnvironment$LocalGE.<clinit>(GraphicsEnvironment.java:84)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:106)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.X11.XToolkit.<clinit>(XToolkit.java:224)
[05:31:39 INFO]: [STDERR]: at java.desktop/sun.awt.PlatformGraphicsInfo.createToolkit(PlatformGraphicsInfo.java:41)
[05:31:39 INFO]: [STDERR]: at java.desktop/java.awt.Toolkit.getDefaultToolkit(Toolkit.java:595)
[05:31:39 INFO]: [STDERR]: at java.desktop/javax.swing.UIManager.getSystemLookAndFeelClassName(UIManager.java:667)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.gui.ServerGUI.a(ServerGUI.java:49)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.dedicated.DedicatedServer.bi(DedicatedServer.java:543)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.Main.lambda$main$2(Main.java:299)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:326)
[05:31:39 INFO]: [STDERR]: at net.minecraft.server.Main.main(Main.java:286)
[05:31:39 INFO]: [STDERR]: at org.bukkit.craftbukkit.Main.main(Main.java:302)
[05:31:39 INFO]: [STDERR]: at io.papermc.paperclip.Paperclip.lambda$main$0(Paperclip.java:42)
[05:31:39 INFO]: [STDERR]: at java.base/java.lang.Thread.run(Thread.java:1589)
[05:31:40 INFO]: Stopping main thread (Ignore any thread death message you see! - DO NOT REPORT THREAD DEATH TO PAPER)
[05:31:40 INFO]: Stopping server
[05:31:40 INFO]: Saving worlds
[05:31:40 INFO]: ThreadedAnvilChunkStorage: All dimensions are saved
[05:31:40 INFO]: Flushing Chunk IO