That's been addressed on Github.
As the error message suggests, Object is no longer allowed as a class name.
I think the base class has been renamed to ConcreteObject, but there may be more to it than that.

For issues like this, its always best to get support from the theme developer. They need to update the theme.

JohntheFish >
Thank you for your reply and your suggestions.

As i just want to give a try to this theme (not sure if i will end using it) and looking at the whole desert of support/replies for 95% of the free themes and addons, i wouldnt bother any dev about this with the hope to get a reply in mind.

After 2 months of trying to make my way in concrete5, i can tell you without going too far in the complains, that there is very very few things that works straight away for me.

Obviously i m not a professionnal or advanced dev, on the other side there is more than 2 decades that i m used to learn from myself quite complex peaces of softwares, and going through the whole concrete5 docs and each page of them most of the time leads to read 2-3 years old usefull questions never answered.
i wonder if those users just lost themself during the following weekend hike or are still quietly waiting their reply from the someone somewhere that obviously got the secret knowledge.

Now i have to fix why i cant receive emails from concrete5 (ofcourse i already read the forums posts about it).

Thanks again for you reply John.

When considering any addon or theme, if I don't already know the developer is currently active, I ask a simple question about some aspect of functionality using the 'Get Help' link.

If they don't answer pre-sale, then I can be pretty sure they won't answer post-sale and can make an informed decision whether I can use an 'abandoned' package on my project.

The concrete5 marketplace is better than most. With the PRB reviewing submissions, some of the 'fire and forget' developers who litter the Wordpress and Joomla worlds are weeded out before they get that far in concrete5.

An idea that has been touted previously is an automatic timeout on marketplace packages, where anything owned by a developer who has not been active for N months is automatically flagged as 'UNSUPPORTED' in big red letters at the top of the marketplace page. Then perhaps removed if it doesn't work with the latest core.

We just need the folks at Portland Labs to find time to work on marketplace infrastructure.

@JohntheFish

Some indicator of a marketplace package not being supported is a good idea.

A flag indicator would help a lot.
In the same logic i think it would be usefull to add a kind of flag indicator on forum topics or answers that are not valid anymore for last concrete5 release, because there is a huge amount of 5-10years old threads with obsolete replies (users could add the flag with an admin check step, or only admins and most active C5 devs could handle those flags).

Regarding the marketplace itself and my own experience, here is an homemade and non-exhaustive list of what appears to be working addon or theme and that i couldnt install on 8.3.2 :

Supermint3
Anitya
Vedana

Easy Image Gallery

One of the most weird thing about Anitya is that i cant install it on my last attempts on a local concrete5 install (XAMPP), but when i go back to my online install of concrete5 after 1 month without playing with it (installed for testing purpose few weeks ago) i can see i have Anitya installed correctly, i didnt remember i already tried this one with a succesfull install.
Both concrete5 version are 8.3.2 ofcourse.

EDIT :
it seems that what i describe for Anitya theme is the same things that occurs for other install problems on localhost, so i guess it might be some mysql or PHP config related on my XAMPP install...

i mean, on my online install Easy image gallery is totally working, Anitya theme too, i tried to install community_store addon too on localhost, and i get the same error message :
Cannot use Concrete\Core\Foundation\Object as Object because 'Object' is a special class name

But community_store addon install works fine on my online Concrete5 install.

Any idea if i can fix this to do all the tests locally as if it is my main online install ?

@MattPesquet I'll bet you're using different versions of php between your localhost and your online server.

@Gondwana
Thank you,
i was almost sure both install were using PHP 7 at least, because i installed last XAMPP release with PHP 7.2.1 on localhost,
and i was sure i was using version 7 online because i can see the selected current version of PHP from my webhost cPanel is 7 (other choice is 5.6), but when i open phpMyAdmin of my webhost server it displays PHP : 5.6.30

First i have to get an answer from my hosting, if i understand well there is more chances that the server is really running 5.6.30, but cPanel option is not taken into account.

Then i m not sure what would be the best choice if the 5.6.30 current settings works fine for me online, i m afraid that switching to version 7 could bring issues, at least gives me the same errors for theme and addon as on localhost.
Should i better keep 5.6 online and try to use 5.6 with Xampp, with no fear of a necessary switch to version 7 driven by next concrete5 coming updates ?

Or is it possible it could be some mysql/PHP settings that i could adjust to make it work for both 5.6 and 7+ version ?

IIRC, the current c5 core works on php up to 7.1 but not 7.2. The next release of c5 will be compatible with php 7.2.

Some add-ons and themes fail on php 7+.

@Gondwana

Thanks a lot !
Tho i had C5/Elemental working fine with 7.2.1.

On my hosting service side, i get a strange reply from them, they say my concrete5 install (and all web root directory of my account) use the selectionned PHP 7.0 version from dashboard, even if phpMyAdmin use and displays 5.6.30 because it is running itself on 5.6 for compatibility reasons for all the exsiting accounts i guess.

i will try with 7.1 or 7.0 on localhost to see if everything works the same.

Thanks again !