To me it looks like nibble marks caused probably by hungry little snail or slug.I have a polyscia that got similar marks on a few leaves last winter. I put a few slug pellets on the top of the compost and the damage stopped.Mine is a houseplant, but it goes outside now and then in the summer for some fresh air and rain. I'd guess the little bugger sneaked in then.
This is a complete stab in the dark, but this might helphttps://ask2.extension.org/kb/faq.php?id=729383Happy New Year to you too
If it's really dry inside, putting a fan on the plant will dehydrate the leaves further.I'd just keep it as you have been doing and as the days grow longer and it warms up it should sprout into growth again.See how it fares.But if you have 2-3 slug pellets - there's nothing to lose.
No fertilizer atm as it's not growing, so it won't use it.I'd guess that seaweed extract would be ideal for it during the growing season - just a little every 2-3 weeks. If you don't' have that any gen. purpose liquid fertilizer will do, but only when it's growing.Go lite on the ferts. too or the new growth may get soft and you want a nice sturdy tree.Best of all get it outside when it warms up so it can enjoy the breeze, rain and sun