Did shamir gave the option to have just a single share? Have you tried it and it worked? At least you suppose to have 2 or shares. If it is a single share, then what is the point of having shirmar as a backup plan.

If you do not need shamir purpose of backup, then just go for normal sees phrase backup directly. Go for segwit derivation path instead and not legacy. With segwit, you can save money on fees while making transactions.