If you want to be able to read on both Windows and Linux formats for external HDDs, format the external HDD in FAT32 format. That’s how I do it for porting games from my Win10 machine to the HDD and then plug it into my Lakka unit and have it pick up the ROMs/ISOs/Images. There are programs out there capable of formatting drives larger than 32GB (fat32formatter for windows is the one I use and of course, it’s free). You should be able to format up to 2 TB drives with it (I have done so successfully with Seagate and WD drives to use with Linux-based PCs and retro gaming distros).
NTFS is also another file format that can be read with Lakka, etc., but will impact speed and performance, so stick with FAT32.