There is no legitimate, functioning "NSP to XCI converter online." If a website claims to offer it for large files, it is a honeypot or a scam.
Why Convert NSP to XCI? The Ultimate Guide to Switch File Formats Nsp To Xci Converter Online
: While older, some custom firmware (CFW) setups historically preferred XCI for "cartridge" loading. There is no legitimate, functioning "NSP to XCI