This could be due to the files still being kept in APFS snapshots created by Time Machine, so you could try running the following in Terminal to clear some of them:
tmutil thinlocalsnapshots / 1000000000 1
The documentation for “tmutil” can be read using the command “man tmutil”, it says:
thinlocalsnapshots mount_point [purge_amount] [urgency]
Thin local Time Machine snapshots for the specified volume.
When purge_amount and urgency are specified, tmutil will attempt
(with urgency level 1-4) to reclaim purge_amount in bytes by
So the above command thins the snapshots on the Mac’s internal drive (which is normally mounted at the path “/”), to reclaim 1GB (1,000,000,000 bytes) with urgency level 1.
The output of the command will list the snapshots it removed. In this example output, 1 snapshot was removed:
Thinned local snapshots: