If you want to modernize the storage for that old PC, then Lo-tech is probably a good choice. They've got a wonderful all-in-one card that includes a mounting bracket, fits into an 8-bit ISA slot, and accepts a CF card directly: https://texelec.com/product/lo-tech-xt-cf-lite-rev-2/
File transfer can be done a number of different ways, including serial ports (USB to RS-232 adapters generally work fine), floppies (USB 3.5" floppy drives are awesome and cheap), and: Networking.
Around the turn of the century, I briefly had an already-old XT machine that had no hard drive, but it did have 10BASE2 Ethernet and Hercules-compatible graphics built into the motherboard.
It was a fun little adventure to get it online with my then-modern LAN and I did a number of unlikely things with it (including a graphical web browser), but the most practical thing it did was connect to a Samba share on my Linux box. It worked great. Old 8-bit network cards are not particularly expensive.
It all depends on how far down the rabbit hole you want to go. :)