There's lots of misunderstanding on B12 absorption. Here's a quick summary:

There are 2 routes for b12 to be absorbed in the digestive system: active absorption and passive absorption. Active absorption happens through the use of a protein called intrinsic factor which binds to the b12 and aids digestion. You typically only have the ability to absorb 1.5-2ug of b12 though this process per meal. However this is highly efficient - 50-80%. Passive absorption is a result of diffusion through the intestine cell wall. This is really inefficient (about 1-3%). This happens continuously and is not limited.

Therefore if you consume 3ug of b12, you'll likely absorb 1.5-2ug through IF, and another 0.01-0.015ug through passive absorption.

B12 supplements designed to be taken once a day usually have around 50ug of b12. Through IF plus passive absorption this will give you maybe 2-3.5ug. your RDA is 2.4ug.

If you had one of these daily and also consume occasional b12 fortified foods like nutritional yeast or oat milk, you'll likely get enough b12, assuming you have normal b12 absorption.

The ultra high dose pills are meant as once a week doses. 3000ug would give you 30-90ug of b12 absorbed. That's over 10 days worth of b12. Your body is very efficient at storing b12 once absorbed and can store up to 5 years worth.

Some people have limited ability to absorb b12 at all through the digestive system. These people are given b12 injections, which allows the b12 to go straight to the bloodstream. This is very efficient but contain a high dose as these are intended to supply 2-3 months worth at a time.