macOS BIg Sur v11.1's TM likes to do huge back ups to the new USB3 Seagate 5 TB HDD?

[Ant]

Hello.

I started a brand new Time Machine (1 partition is using encrypted APFS for TM;
other 2 are for exFAT for now) back up late last night. I started its first one
that took a long time (almost 400 GB of datas out of 2 TB). After it was done,
I unmounted and then disconnected.

I reconnected about 30 minutes ago to do another manual back up, and noticed it
was doing a long back up! What the heck? I thought it is supposed to do
incremental back ups like the old macOS (e.g., Mojave v10.14.6 and earlier)'s
TMs. Did Big Sur's TM change something?

Thank you for reading and hopefully answering. :)
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