Hi and welcome to the community!
A quick search comes up with details of the charging port shows it is USB and "standard wall outlet or a USB port on your computer" implies nothing special so a lower-end charging type.
It doesn't say how big is the internal battery but "12 hr., typical usage"
So to work out the size of an Anker Powercore we have to calculate it from how long you want it to work.
The information says it will work for 12 hours and you said you wanted it to work up to 12 hours so you're talking a fully charge device is just about able to meet your needs and you need relatively little say to double its life. If we knew how big was the internal battery we'd be looking for something of the same size, but we don't have that information.
One way to do this is a buy a meter, now as your first investment. You can get a meter which accumulates how much current went into the device from empty to full and then you know what size battery to get. Buying a meter is in general a good thing to own for lots of reasons.
If you don't want to buy a meter and measure, then its pure guesswork. Seeing as you are already close to a full day, implies you need something small. The 6700 you mention would be probably sufficient.
The Speed 10000 is overkill, the information above says it does not support Qualcomm Quickcharge so unless you also want to charge something which has QC like a Samsung phone then you're paying over the odds. The Powerbank+ is also overkill for the same reason. The non-QC level up is simply called the Powercore 10000.
So unless you want to also recharge other things like a mobile phone on your bike as well then its a choice between the Astro 6700 and the Powercore 10000. How many recharges of the Garmin they do - we can only guess.
As the Garmin is looking physically fairly small, that tells me it probably has a small battery and my gut is the 6700 is going to be 1 to 1.5 recharges so give 12 to 18 hours of use (above the 12 hours of the builtin battery). A meter could tell us more precisely.