Resourcepacks
Resourcepacks are purely client sided, and it only affects client related aspects, such as item/block models, translations or textures. A resourcepack cannot affect server specific aspects such as loot tables, tags or advancements.
This is not a full featured resourcepack tutorial and basic datapack knowledge, such as file, pack or id formats, are assumed.
For more info regarding resourcepacks you can read Minecraft Wiki's page about them.
Minecraft Wiki also has a wonderful and easy to follow tutorial on how to setup and build a resourcepack which you can find here. With the very important mention that Minecraft 1.16.5 has a pack_format of 6.