>>240です
下記で状況を再現してみましょうか？
$ mkdir lineage-curtana && cd $_
$ repo init -u git://github.com/LineageOS/android.git -b lineage-17.1
$ mkdir -p .repo/local_manifest
次の行（<<EOFを含む行）からEOFのある行まで一度にターミナルに貼り付ける
$ cat <<EOF > ./.repo/local_manifest/Redmi-SM6250.xml
<?xml version="1.0" encoding="UTF-8"?>
<manifest>
<remote name="Redmi-SM6250" fetch="https://github.com/Redmi-SM6250"; revision="lineage-17.1" />
<project name="android_device_redmi_sm6250-common" path="device/redmi/sm6250-common" remote="Redmi-SM6250"/>
<project name="android_device_redmi_curtana" path="device/redmi/curtana" remote="Redmi-SM6250"/>
<project name="android_vendor_redmi_sm6250-common" path="vendor/redmi/sm6250-common" remote="Redmi-SM6250"/>
<project name="android_kernel_redmi_sm6250" path="kernel/redmi/sm6250" remote="Redmi-SM6250"/>
</manifest>
EOF
結果の確認
$ cat ./.repo/local_manifest/Redmi-SM6250.xml
repo sync開始
$ repo sync -j8 -cv --no-clone-bundle --no-tags