Bukkit

In reply to WreckItFelix:

 Yes. OpenInv doesn't apply slot restrictions, so you can place and remove whatever wherever. Put dirt on your feet, take off curse of binding gear, anything.

In reply to skondras_l:

 Sorry, I don't know what Aternos is - I haven't actually played Minecraft for any reason other than testing in the past few years. Note that OpenInv is only for Bukkit servers, so if Aternos is some kind of Forge or other server variant it won't work. Assuming it is a Bukkit-compatible server, I recommend installing LuckPerms for your permissions plugin.

You don't necessarily need a permissions plugin to use OpenInv, but you will have to be an op if you don't install one.

In reply to Blutrecht:

 OpenInv is already functional on 1.16.5 - it was a minor update from 1.16.4, and did not affect anything OpenInv uses. If you are encountering issues accessing offline players' inventories, make sure you have your permissions set up properly. Specifically, you may have denied yourself OpenInv.openoffline by accident.

In reply to CosmicSocietySonic:

 Unfortunately, can't help you with so few details. I haven't heard of anything like that happening in years, so if you could get back to me with your server version (not just 1.16.5, actual implementation and build number or commit hash) and OpenInv version, that would be great.

In reply to CosmicSocietySonic:

 Sounds like an incompatibility with another plugin unfortunately. I'll double check the 1.16.5 diff, but I did re-check everything with the last revision change. OpenInv doesn't have a concept of per-world inventories because Minecraft doesn't have a concept of that. Ideally your per-world inventory system should offer its own inventory/ender chest editor.

In reply to sandpog:

 From the description: "Some other nice features of the plugin include the ability to access the armor slots of player inventories"

In reply to sarcasmkekw:

 The plugin works fine without other plugins installed, which means its permissions are working as intended with the presets provided for Bukkit's inbuilt SuperPerms system. Unfortunately, due to the number of variables involved, it's extremely difficult diagnose your permissions problem. Your best bet is to use a system such as LuckPerm's verbose mode that tells you real-time what permissions are being checked for whom and how they evaluate. If you can provide enough information to indicate an actual issue I will be happy to look into it, but until such a time the sheer number of things that could be wrong make it impossible to help you.

Tl;dr: You have likely misconfigured your permissions.

In reply to SushiKarasumori:

 You can use Bukkit's commands.yml feature to resolve command conflicts.