hi… i ve 2 sd cards, the 1st one used to launch raspbian, the second one for Lakka… Is there a way to have one only sd to choose the OS I need? Tx for help!
dual-booting is possible, AFAIK, but a pretty significant hassle, such that it’s usually easier to just physically swap the cards.
Do you know how? For me it’d be great have everything in one sd card only! tx…
Thank you , Hunterk!
Edit: I see that unfortunately these ways don’t work with raspberry pi 4… 
Hello Irishman! If you set a new sd card with NOOBS at some time in the process, you can choose what os you want and you can multi select raspbian and lakka together. The system install a boot GRUB automatically. So you are two problems, first the sd card size will be equally divided so 64 gb become 32/32 a waste for lakka and second you must re-set raspbian and lakka.
I use xubuntu on my laptop and resize my sd card with g parted on windows or mac I don’t know.
Well… about the size, I could use a small SD… 4gb is enough? Or better 8?
About re start both OS… never mind… 
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Hi @irishman, have you considered the option of building Retroarch on Raspbian and using just one OS?
Unfortunately I can’t guide you through the process, I have a Pi 3B but the Pi 4 has enough differences that change how it should be built (the cores too it seems).
8 Gb is very little almost 16 but 32 is strongly recommended. My raspbian after some installation e files is 18 Gb… I also have to try the repository version, strangely I’ve never used it, but I guess it’s old.
Yes, you can use NOOBS or PINN (recommended) both very easy to use, and you can download OS from there, try them.
Actually I’ve got a card with Raspbian Full + LAKKA + LibreElec and it works like a charm.