ANY instrument is challenging when first learning it (for reference" I play 5 of them at various levels). Although some things do transfer over, like the plectrum from guitar to mandolin, or fingering technique between banjo,guitar & mando, or the tuning of mando and fiddle, there are still enough differences to make each one a challenge in itself.
Learning, in itself, is a learning experience. It takes a while ot figure out how you learn best. Tab,notation, by ear, visually…all are possible tools, but they don’t all work as well for each person. Time management, concentration, endurance, dexterity, and attentive listening, all play a part in the learning process, and all take time.
We all learn at different speeds and the thing to keep in mind is 1( if you put in the effort you will make progress (which is really the goal)…and 2) you’re doing it for FUN and enjoyment…there is no make or break test upon completion…