already shut down RSS DHT and channel.The other BT clients are less than tixati.

What is the biggest file in your Tixati profile catalog? channels2.dat? How much is it exactly?

If you have used torrent cache channels, you need to remove them from the local list to delete their data. If you see millions of shared files in the status column, your client still stores it. Fully stop the program to be sure. After next gather they re-appear, but remain empty if you don't connect.

Other possible reason is having a lot of torrents with tens of thousands of files.

Probably just a matter of using the RAM available, offload the hard disks. Or is your total free RAM below, say, 5GB?

RSS was turned off，nothing downloads and uploads，the rest space of disk is 50 Gib，still 750 Mib memory，2 times than Bigly BT 4.0.0 with JAVA 25 (64 bit) Eclipse Adoptium with also thousands RSS not auto download，qbittorrent 5.1.4 is much less than other BT clients.