See https://www.cnx-software.com/2021/09/29/heatshrink-an-ultra-lightweight-compression-library-for-embedded-systems/ (https://www.cnx-software.com/2021/09/29/heatshrink-an-ultra-lightweight-compression-library-for-embedded-systems/)
It needs as low as 50 bytes of RAM (usually 300). It's based on LZSS.