A mod that lets players toggle PvP individually, while offering some neat extra features that I reckon you may find useful. I am also aware that quite a few mods do something similar, but I felt like I could make something beyond a simple toggle.

• PvP preferences: Players choose whether to disable or enable PvP for themselves, which is persistent on server restart (things like combat flags, cooldowns, and the global PvP state are not).
• Colored name tags: Uses vanilla's teams to show off players' PvP states.
• Combat flagging: Works by temporarily disabling toggling upon engaging in PvP. Players who are flagged will be immediately killed when attempting to log off while they have an active combat flag. It does not account for how the player got disconnected (say, by losing connection) to avoid potential workarounds.
• Global PvP: Force PvP on or off for all players server-wide; this takes priority over everything else.
• Pet protect: Protect all tamed mobs from players whose PvP is off. Attackers are flagged upon damaging a tame (the pet owner’s PvP state is not factored in). Feel free to turn this off if you'd rather use a dedicated mod to handle this.
• Forced PvP in other dimensions: Forced PvP in any dimension that isn't the Overworld.
• LuckPerms support: Allows you to customize accessibility to things.
• Configurability: Some stuff can be configured; for info on what is configurable, go down to the configuration section.

This mod ignores the pvp setting in server.properties. Stick to the newest versions of the mod, as older versions may have bugs or lack features as my work is not perfect. Make sure to look at the dependencies section as well.

• Fabric API
• LuckPerms (This is entirely optional if you don't care about customizing permissions).

{
  // WARNING: DO NOT COPY THIS EXAMPLE JSON
  
  // Cooldown for toggling
  "toggle_cooldown": 120.0,

  // How long one is flagged for after engaging in combat
  "combat_flag_duration": 60.0,

  // Default PvP preference for new players
  "default_pvp_preference": true,

  // Console feedback
  "broadcast_to_other_ops": false,

  // I reckon the rest is self-explanatory
  "punish_combat_log": true,
  "protect_tameables": true,
  "force_pvp_in_other_dimensions": false,
  "team_colors": true
}

Thank you for downloading. I would really appreciate it if you could report any potential issues you encounter in the comments section of the CurseForge mod page, as I currently have no other way to receive feedback.
You can also support me by sharing the mod around, as it really motivates me to work on it when there are people benefiting from its usage, no matter how small.