As best I can tell, virtual filesystem support on baremetal targets was effectively removed by https://github.com/tinygo-org/tinygo/commit/a680bfbb7afcb424c4d8110255336f85fd66e7e6 NewFile in src/os/file_other.go always returns a stdioFileHandle now (https://github.com/tinygo-org/tinygo/commit/a680bfbb7afcb424c4d8110255336f85fd66e7e6#diff-639e6d3c80d353b492953bcbd0b3eec979e6c88a776684acd1ac961b6217e24eR36) and should be refactored to delegate a mounted virtual filesystem if it exists.