Use mcetool.

Yes, I agree, it's not very user-friendly to do it on the command line.

The same tool can also let you set "double tap to unlock", but it's not advised if the phone is just laying around in your pocket (risk of auto dialing something) instead of stashed into a holste or a case.

That is weird, I've exactly used such card in the past, without any problems...

A few question :

When formating the card as EXT4 in the laptop :
- did you use modern GPT partitionning ? or an old MBR style ? (I've only tested GPT myself)
- did you took time to change the access rights (by default root) ? you need to change them to the nemo user (laptop: "chown 100000:100000 /run/media/<whatever the mount point of your card>", or if mounted on the Xperia : as root "chown nemo:nemo /media/sdcard/<UUID of the partition>"

When you have the card inserted :
- what does 'mount' terminal command say ?
- is there a started sd-mount@mmcblk1p1.service ("systemctl") ? what's its status (as root, "systemctl status sd-mount@mmcblk1p1.service")
- have you tried mounting manually ? (as root : "mount -t ext4 /dev/mmcblk1p1 /mnt/sdcard")
- notice anything funny in the recent logs ? (as root : "journalctl --since '20 min ago' ")

And the most obvious question :
- You did buy it retail ? not on e-bay from some guy who sells them at 50% off ?