There are no problems compiling other plugins. In the same way, so I don't suspect any misconfiguration on my end.
$ git clone https://github.com/promcteam/promccore.git
Cloning into 'promccore'...
remote: Enumerating objects: 1417, done.
remote: Counting objects: 100% (1417/1417), done.
remote: Compressing objects: 100% (770/770), done.
remote: Total 1417 (delta 696), reused 1170 (delta 450), pack-reused 0
Receiving objects: 100% (1417/1417), 451.86 KiB | 2.32 MiB/s, done.
Resolving deltas: 100% (696/696), done.
$ mvn clean package
[INFO] Scanning for projects...
[INFO]
[INFO] -----------------------< mc.promcteam:promccore >-----------------------
[INFO] Building ProMCCore 1.0.3.8
[INFO] --------------------------------[ jar ]---------------------------------
[WARNING] The POM for io.lumine.xikage:MythicMobs:jar:4.9.1 is invalid, transitive dependencies (if any) will not be available, enable debug logging for more details
[WARNING] The POM for org.mcmonkey:sentinel:jar:2.2.5-20210408.112621-407 is invalid, transitive dependencies (if any) will not be available, enable debug logging for more details
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ promccore ---
[INFO] Deleting /root/ProBuilds
[INFO]
[INFO] --- maven-resources-plugin:3.1.0:resources (default-resources) @ promccore ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 10 resources
[INFO]
[INFO] --- maven-resources-plugin:3.1.0:copy-resources (readme) @ promccore ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ promccore ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 272 source files to /root/ProBuilds/classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/api/meta/NBTAttribute.java:[3,28] package org.bukkit.attribute does not exist
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/api/meta/NBTAttribute.java:[4,28] package org.bukkit.inventory does not exist
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/api/meta/NBTAttribute.java:[48,19] cannot find symbol
symbol: class Attribute
location: class mc.promcteam.engine.api.meta.NBTAttribute
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/api/meta/NBTAttribute.java:[51,52] cannot find symbol
symbol: class Attribute
location: class mc.promcteam.engine.api.meta.NBTAttribute
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/api/meta/NBTAttribute.java:[63,12] cannot find symbol
symbol: class Attribute
location: class mc.promcteam.engine.api.meta.NBTAttribute
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/api/meta/NBTAttribute.java:[68,34] cannot find symbol
symbol: class EquipmentSlot
location: class mc.promcteam.engine.api.meta.NBTAttribute
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/manager/api/gui/JIcon.java:[4,18] package org.bukkit does not exist
[ERROR] /root/promccore/src/main/java/mc/promcteam/engine/manager/api/gui/JIcon.java:[5,31] package org.bukkit.enchantments does not exist