I'm guessing that what you're seeing is a 128 MB/121 MiB boot partition. It's likely that the main partition is using an ext4 filesystem, and as far as I know (I haven't used Windows for ~10 years) Microsoft has choosen not to support this filesystem (since support would make it easier for Linux-based and Windows-based computers to co-exist, which is of course a threat to MS.)
My Mobian SD card actually use ext4 for both boot and main partitions, so Windows would probably show that card as having no valid partitions at all.
There are apparently 3rd-party tools for accessing linux file systems from Windows, but I'm not familiar with them/don't know how well they work. A better option might be to install and dual-boot linux on your PC and access both your SD card and your Windows NTFS file system from the Linux OS.
My Mobian SD card actually use ext4 for both boot and main partitions, so Windows would probably show that card as having no valid partitions at all.
There are apparently 3rd-party tools for accessing linux file systems from Windows, but I'm not familiar with them/don't know how well they work. A better option might be to install and dual-boot linux on your PC and access both your SD card and your Windows NTFS file system from the Linux OS.