Why time machine backup more space I need?

Tried to use my new iMac desktop and transferred all my data and app from the old MacBook Pro laptop. Used time machine to do a full backup on my external hard drive, and it shows the backup size is less than 100GB. Then use “migration assistance” tool to do restore on iMac, but shows not enough space for restore. I have 250GB storage equipment on iMac and have a fresh Monterey installed, so, it should be well enough for this migration, right? I tried to use Diskwave tool to check library further and found “one drive” reported over 169GB space occupied, that’s weird as this is online app, it should not use my local hard drive space, isn’t it? I then exclude it in time machine menu and redo the back up, however, it still reported the same error. I attached some pictures I took, can someone give some clue what I could do wrongly here? Many thanks.