The screenshot you attached is unrelated to any «plugin».
It is related to Magento itself.
To do any work with the Justuno module, I need to set up Magento first because a Magento module works in Magento environments only.
I preserved all my previous Magento environments (2019-2023) which I used to develop the Justuno module.
Still, as I did not work with the Justuno module for a year, then it is better to ensure that any modifications in the Justuno module (and even the Justuno module in its current state, before any modifications) still work correctly with the latest Magento version (and with PHP 8.3, which can be used to run the latest Magento version).
The email sending bug (mage2.pro/t/6392) is not related to the latest Magento version, I just ensured that it had been solved in the latest Magento version, and skipped my patch from my Magento environment for Justuno (https://github.com/justuno-com/test-2.4.7-p1/blob/main/.gitignore.
It is just as a high-quality software development process is implemented:
a reusable module needs to be tested with the latest stable version of the environment where it is intended to be run.
issues of the environment itself need to be carefully counted and documented because they could affect the module in different ways (e.g., the «Environment emulation nesting is not allowed» failure could affect not only emails because the «environment emulation nesting» can be used in Magento in different contexts).
My mage2pro/core package is a middleware between Magento and my end-user Magento modules.
I have made over 9000+ commits to it since 2015, and it is the biggest and the most complex Magento work in my career.
The middleware ensures that any Magento task/problem I encounter in my career:
Is solved only once.
It is compatible with all environments I encounter in my career (all Magento versions, all PHP versions, all operating systems, Apache, MySQL versions, Elasticsearch versions, all filesystems, all hosting providers, and so on).
Is solved in the best possible way I found in my Magento career.
E.g, I could find a solution in 2010, then a better solution in 2015, then an even better solution in 2020. Thinking of the same problem again and again, I am discovering the best possible solution for problems.
Is documented in a single place, so I do not need to remember why in 2010 I chose a particular decision for a particular Magento problem.
The Justuno module does not use my mage2pro/core package since 2020 (by your decision).
The Justuno module uses a similar justuno-com/core middleware which I produced in 2020 by removing all code not used by the Justuno module from my mage2pro/core package.
The justuno-com/core package is used only by the Justuno module, and I work on the Justuno module once a year, so it is not as up-to-date as mage2pro/core, and many problems are solved using my experience until 2020 (though I upgraded justuno-com/core in 2022 and 2023 to make it compatible with PHP 8.0, 8.1, 8.2).