Different apps with different firmware?

I would like to ask for advice - or explanation (I don’t understand it)

Why aren’t applications with different custom firmwares compatible with each other and cause the device to reset when trying to run it?

For example - I would like to use applications that are in firmware version A on firmware version B.
Because in version B they are not included “in the package” - what to do in such a situation, where to look for compatible ones?

At first, FW A or B will not be supported here. Only the official one.
If you have an app that needs custom features, you are out of luck. If you’ve seen an app in a CFW, that is interesting to use in OFW, nearly all apps (I haven’t seen) are open source. Just download and compile it.

But this is so general, that you may have issues with the first point (needs functions behind OFW).

The short answer is the Flipper only has around 700KB for it’s firmware so backwards compatibility can’t always be achieved and cross compatibility isn’t always possible.