Found that also myself trying to do the same thing haha. I did the same process as OP, gparted took 2.5 hours in my 1TB HDD to create a new partition, then copying the data from old to new partition was painfully slow, so I went to copy it to another dive and into the new partition.
Afterwards I deleted the old partition and grew the new one, which took a bit more than 1.5 hours.

If I had the space I would have copied all the data out of the drive, formatted it and then copied back into. It would have been quicker.

Yesterday I started looking for mini pcs and found this post https://www.reddit.com/r/MiniPCs/comments/1afzkt5/2024_general_mini_pc_guide_usa/

They shared this link which contains data on 2.8k machines, it helped me compare some of the options I was looking for and find new ones.
https://docs.google.com/spreadsheets/d/1SWqLJ6tGmYHzqGaa4RZs54iw7C1uLcTU_rLTRHTOzaA/edit

Sadly it doesn’t contain data bout the ThinkPad, but I might as well share in case you’re willing to consider other brands.

Edit: Oh, wait, I was thinking about a ThinkCentre, not a ThinkPad :P
Well, I’ll leave this around in case someone finds it useful, hehe.