installing 2.3.0

the problem is that I returned to the JEM 2.2.3 version, in order to keep my website functional. So I cannot experiment anymore. Is it possible to install two versions of JEM on the same site together?

No, that is not possible.

The only possibility is to take a backup of your Joomla installation and restore it locally. Then perform an update to JEM 2.3.0 and do the tests.

It's important your local apache / PHP enfironment uses the same PHP version.
I use Laragon for this, to easily switch from PHP version

Hi, I updated on 3 different sites and had no problems with Joomla 3.9.16 and php 7.3 and 7.4.
My question: Did you use any overrides who could disturb now the new JEM core?

I have now tested JEM 2.3.0 on another website. The tablestyle looks better than the responsive style, so at first I see no advantages of JEM 2.3.0. I will stick to JEM 2.2.3 for now. Maybe some bugs will be found in future.

Just a question...:

Why don't you stick to 2.3.0 and set the style to 'legacy'? that should leave your frontend just like it was in JEM 2.2.3, but you will still be on the latest version.

Please read the help for JEM responsive in the help:
Try with Settings>Layout>Table Width in % ->best is: this must be empty!!!

@ernst67 and others: this should be the default!