I’ve tried komga and kavita both, but didn’t find them very useful. Nowadays i just copy the files downloaded from nyaa to my kobo, where i read them with koreader. Its possible to sideload it on kindles, but its tricky. Koreader even has OPSD support, in case you want to use kavita/komga. But for most random/weekly reading I use Kotatsu on my tablet/phone, as it has a sync feature (you can even selfhost your own sync server!). For ebooks I also just use my ereader. I have no need for a bulky management system. I hope this helped you somehow. Good luck!