Already modified 5 or more clonemental pages from 8.5.x to 9.0.x. Overall, it is not very difficult. I used files from the elemental template provided in version 9 (e.g. page_theme.php, header, footer elements, main.js and some others). And for the blocks to work well, boostrap 3 needs to be changed to 5 (bootstrap-modified.css file in elemental). In my case, I just downloaded the file from the boostrap website and added a few modifications. Later in page_theme.php I also changed the Grid Framework to Boostrap 5. Now everything works fine (blocks, grids layout etc), even on php 8 I didn’t find many problems with basic block use. I haven’t tested everything 100% yet, but at the moment everything works fine for me after making the changes.
Many thanks @lukasznillo@JohntheFish for providing help. This is great! My new v.9 Elemental clone works. I even tried with an atomik clone and added a «shim» as @JohntheFish suggests in another thread. That works too.
In some blocks the wysiwyg editor behaves strange. My classes added in pagetheme do not work. Any idea? Has it anything to do with bootstrap?
Thanks @JohntheFish, but I could not find anything in Github. Whatever causes ckeditor not to work, I hope it will be fixed in 9.03. Everthing else runs smooth. Like @lukasznillo I’m not able to check all blocks.