What are your plans for Bootstrap 5. Will it break compatibility with Boostrap 4?
In short, yes we will support Bootstrap 5. Will it break compatibility: I'm not sure yet. Currently, BS 5 is in beta, it does not use JQuery any more, although JQuery still can be used. There is a new devicecontext (xxl) and more things has changed.
We have been looking at BS5 obviously, but we can only start implementing when the used components are compatible with BS 5. Currently, that is not (yet) the case. That might lead to change of components, properties, events.
On the other hand, you don't have to fear that your applications will not work any more. We will be supporting BS4 AND BS5, so you have a choice.
BS is promising that the migration of 4 to 5 is more easy then 3 to 4. We have been supporting BS3 but deprecated that because PHsPeed was still in beta when BS 4 got the lead. We were able to maintain compatibility because the compiler generates the appropriate code. Ie. BS3 used panels, BS4 cards. But is was not so difficult to make that transition, so that's why PHsPeed still uses the Panel component. It did not break projects, but did generate other code. That's something we will always try.
So as soon as we support BS 5, I would start new projects with BS 5. If you have older systems in production then you have the choice of keeping them under BS 4 (BS3 is still very much used today) or slowly migrate them to BS 5.
Hope this answers your question. No need for concern.