As I found Joomla 4 will use Bootstrap 4 and CSS GRID, second one will be used for frontend templates. More details here
At the end in Summary I read this recommendation :
If you're building a template in Joomla 4, or are creating the frontend layout for an extension, don't rush into using Bootstrap 4. You should consider relying on CSS Grid instead.
How it will affect on Cobalt future version? Will we get same headache as now with BS2 and BS3 ?
As I found Joomla 4 will use Bootstrap 4 and CSS GRID, second one will be used for frontend templates. More details here
At the end in Summary I read this recommendation :
How it will affect on Cobalt future version? Will we get same headache as now with BS2 and BS3 ?