Hi. Are you boxing things up just to box them up, or are you separating by category, like donate/toss(to actually take a trip out to the trash…asap)/etc?
I recently cleaned out my deceased father’s house. There really wasn’t a better way to deal with his stuff than to sort it on-the-spot and deal with it. Some things like “important papers” went home with me to go thru in relative comfort. Some days I started out with a run to Goodwill, others a recycling center run. Not that you have that kind of mess, but every day I saw progress…and that felt good. On days I woke up lazy, I reminded myself about that positive feeling.
For what clutter I have (of my own) there are days/hours/minutes when I “get brutal”, meaning I “just do it”… Articles of places I’d like to visit and can realistically vs. “by the time I’ll be able to go there I can google it” recycling bag filler. Socks sorted. Undies culled. Usually a little at a time, otherwise I will get overwhelmed and frustrated and lose motivation.