Unconfirmed transaction: the status is "0 / unacknowledged, not in memory pool "
The transaction you made is quite large, so also if the fee you paid is not low in absolute term, it is in relation to the space taken on blockchain.
0.00120000 / 11767 = 0.00000010

you have paid 10 sat/vByte that was borderline to be included in a block in the days you should have broadcast the transaction.
As you can check here:
https://jochen-hoenicke.de/queue/#BTC,3m,count
there are some transaction with a fee rate similar to your that have been verified (note that it generally takes 14 days for the transaction to be removed from the mempool if not confirmed), so i'm not 100% sure the fee rate is the reason because your transaction has not been verified, maybe there is another reason (eg. when you made your transaction your client is not fully synchronized and you close bitcoin-core before the transaction was actually submitted).

What should I do in the future?

Be sure that your client is synchronized or at least check on a blockexplorer that your transaction just submitted is in mempool (although not yet confirmed).
Enable Replace By Fee so if the fee you set turn out to be too low you can raise it later.
You can also use the bitcoin-core fee estimation choosing recommended transaction fee and setting a confirmation target no longer than a few hours.
Remember to check that the transaction has been verified before 14 days have passed since its submission.