Sorry for the late response. The pack works fine on Minecraft 1.18.1, you only get the message because the pack still has the old resource pack format set for Minecraft 1.16 and so Minecraft can't make sure that the pack is actually compatible.

If this bothers you, you can unzip the zip file, open the pack.mcmeta file in the root directory of the pack with a text editor and set the pack_format to 8.

The downside of this (and reason why I haven't updated the pack yet) is that Minecraft versions with a lower format number will then not load the pack anymore, even though there was no change to the packs content and it would still work. In future Minecraft versions, it may of course be necessary to actually change something in the pack again, but so far the changes have not been relevant to the content of this pack. If you're interested in this topic you can find a history of most changes that have led to the increase of each number in the Minecraft wiki.

Thanks, I heavily suspected this to be the case, but I didn't know enough about resource pack changes to know this for sure. <3