I did an UEFI install in BTFRS not long ago. Using Gparted, I just made an ESP partition of 100MiB in size and formatted as FAT32. Then I made another partition formatted as BTRFS for the system.
In the installer I chose manual partitioning and pointed the installer to these newly created partitions.
Mark each partition and click on edit.
For the ESP choose /boot/efi as mount point and flag it as boot.
For the system partition mount it at /.
That’s it. Click next and you should be good.
This is the thread I got some invaluable help and advice on setting up my system. But I had already installed it. Anyhow here it is :
You might want to take a look here as well:
https://endeavouros.com/docs/installation/calamares-offline-installer-tips/