At least that is the only package required in Plasma. Windows 11, Mac and Ubuntu (since 20.04) have HEIF support OOTB. HEICs are the standard image and video format for all Apple Devices. They take smaller space but have higher quality than JPEGs.
More Info Here.
We already include kimageformats5 with a KDE/plasma install.
As for libheif, our goal is not to have support for everything in the base install.
We want things to generally work out of the box and the system to serve as a base for people to install the packages they want.
There is no perfect list of packages that will please everyone. No matter what we select, someone thinks things are missing and someone else complains of bloat.
That is why we try to have a functional base and let the individual build on top of it.
How can I add HEIC thumbnails in Thunar (xfce, tumblerd) ?
Use Dolphin instead. I kid. 
But these may be of help:
and
According to the 2nd thread, it looks like there’s a bunch you’d have to do to get it to display in Thunar. Meanwhile, the two best file managers on Linux (Dolphin and Nemo, in my experienced opinion) just work.
Of course, I understand that you may want to use Thunar because it is extensible, and as such the “bunch you’d have to do” may actually be okay with you.
However, if it’s just a case where you don’t want to use KDE/Qt-based apps, then Nemo is GTK-based - it would fit in well as an alternative/replacement for Thunar. And if just using anything that works is all that matters to you, then Dolphin can be downloaded separately from KDE, so you wouldn’t be installing a whole DE.
I’m currently using Dolphin as my main file and media manager even though I know XnViewMP is better at media management.
Your choice in the end.
EOS is supposed to give you a basic arch system Out Of The Box. You then install stuff you want yourself.
Nobody cares what Windows 11, Mac and Ubuntu are supporting. EOS is not competing with them.
Are you sure an arch based linux distro (where you have to install and setup things for yourself) is your thing?
Thanks for the answer, I discovered it was already working with HEIC files, I just had a few .HEIC files that were jpeg with the wrong file extension.
if you have the package libheif it works out of the box in thunar
/usr/share/thumbnailers/heif.thumbnailer is owned by libheif 1.17.6-3
Well, both threads I sent were about 3 years old, so it makes sense that they’d fix/integrate it by now.
What’s stopping you from just installing it manually yourself once? If it’s optional inside the installer, you can just simply install it yourself after installing EOS.
Shouldn’t this have been 
Just sayin’, so to speak 
Maybe not. Just realised that it was @kIERO who said they found a solution, not the OP @amethystgosling
So, @amethystgosling has what @kIERO suggested worked? If so, please mark their response as the solution.
EDIT: Just also realised that this isn’t the type of thread that can be “solved” as it’s a request/preference, not a bug/problem the OP is experiencing.
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