Welcome
I'd say my practice is 50% work in my mind and 50% at the keyboard as I'm in the later stages of preparing for a recital. I have a recital in 2 days.Especially the heavily technical stuff, you need to know it away from the keyboard just as you'd recognize blue or red. Muscle memory is always going to deceive you.The initial stages of learning repertoire relies less on memorizing away from the score and piano both obviously.If you're away from a keyboard a week that's an issue, for me practice = confirmation of that you don't know, technical problem solving and ingraining the physical memory which is necessary as long as you don't let it lie to you.
Make sure you set the fingering before going mental - it's about 60% effective as practical. Found the attached on my hard drive.
I'm sure everyone knows the story of Gieseking who learned a concerto studying on the train and chasing butterflies and went directly to the rehearsal without having played one note on the piano. There's a book by lebert-stark with an intro by gieseking explaining his "method". I tried it so many times. I always fell asleep after 5 minutes...i guess it's not for everyone.
I learn all my music now away from the piano first then only take it to the piano once I can perform the piece or a section of the piece in my imagination from memory. This has at least halved the time it takes me to learn new music. It's so effective in fact that I can't believe I used to do it any other way.It's is difficult though and the only thing I can suggest is that you the more you do it the better you'll get a learning this way. Whenever I'm playing in my head I always keep my eyes closed too. I helps the visualisation a lot.