Instead of fully removing the shells, you can try cracking them slightly to
make it easier for your budgie to access the inner seed. This way, your budgie can practice breaking the shells further and gradually develop the necessary skills. While sunflower seeds are a popular treat for budgies, there are other types of seeds you can offer as well. Budgies have individual preferences, so experiment with different seed varieties such as millet, safflower seeds, or hemp seeds. Your budgie may find these seeds easier to eat and enjoy them as an alternative.
I am sorry to say it but I am really not a fan of the link you shared, it is definitely not the best information I have seen compiled for budgies- it advises to feed an awful lot of fruits which we all know is not appropriate for most of our companion birds but especially a parrot who is so small has not evolved to eat a lot of fruit.
I did not read past the "what can budgies eat" section so can't comment on the whole article, but I am a big believer in just because they CAN eat those things does not mean they SHOULD eat all of those things.
If you want access to good information on bird care you will easily find it here on the Avenue. There are so many easy to find links on google that are full of incorrect and iffy information that has been written by basically anyone with a desire to inform the world on what they think, I would rather read information written by someone with valid, proven experience and knowledge- We all need to be careful when scanning online articles for important information such as for care, housing and diets for our companion birds because there are way too many people without a clue writing these articles and so called informative fact sheets.
They absolutely love lettuce. I want to get romaine lettuce since that’s healthier. But I can’t find any. They also love Parsley and anything that’s green.
You can try other green things such as celery tops, carrot tops, broccoli/broccolini, baby spinach- many budgies love those types of fresh foods. My little guy will only eat them if I peg them on the ceiling of his cage near his favorite perch and he prefers them dripping wet (very common with budgies!) Sprouts is another good option.