Now that your card is formatted properly, have you done anything to manually transfer files over to it? Android will not automatically migrates files to the card, so you'll have to do it yourself to free up internal storage.
The proper way to do this is to use the copy command, not the move command. If something glitches and the paste part of the function fails, the copy method retains the original files to try again. The move method deletes the original and holds it in memory until written to the new storage location, meaning data loss if it fails.
The gallery app should be able to do this for all of your photos and videos, typically by long pressing the photo(s) or album/folders to select them, then a menu option to start the copy command. For other things like PDF files or other stand alone files, those would need either their own apps to transfer files or a file browser app that works similar to what you get on a PC.
Once you have verified everything you want is successfully transferred, then go back to those files on internal storage and delete them. You may want to remove the SD card during this process to prevent deleting the new copies on the card.
If you do a lot of text messaging, check for any sort of auto delete option in the texting app and make sure it is on. I ran out of space once in large part due to not auto deleting texts. You should also go through your app manager to see if any apps are running away on storage use. Some social media apps are bad about caching anything and everything, eating up storage space. If you see any with abnormally large cache, clearing said cache can potentially free up lots of space (though may just rebuild it again over time if you keep using them).
It's also worth noting that 64 GB internal is getting to be on the small end of storage these days. I personally recommend 128 GB bare minimum on a phone, and that's only if it has an SD card slot. Since many phones no longer offer that slot, I would recommend 256 GB+ depending on someone's usage. Depending on how much you have going on, this may become a case where it's simply time to consider upgrading to a phone with more storage. Apps only get bigger over time, taking up more of your limited storage, which means this could become a reoccurring problem for you.