One more note.

When I have a dozen of WinSCPs running, the whole system is not that slow, but for ex. if I try to open an xlsx-file (with Excel) or if I try to open Wiondows Search from Windows Explorer, it now takes them about 15 seconds to just start. I know it's their fault but maybe there's something in WinSCP that can be changed to fix that.

Thanks for your suggestion, I'll consider it.

I think many people are satisfied with this aspect but sometimes I am not, so just in case I report this, and this is of low priority, but at the same time easy to implement.

Sometimes I do have to open a dozen of WinSCP windows to update many servers. Then I notice my system slows down. I looked up the process list and found out each of the WinSCP processes consumes 0-5% of CPU. As a result they all operate a little slowly, for ex. when I switch to any of the windows, execute a command and the remote file list is refreshed this all is done noticeably slower than usual.

I realize this is not a frequent case but maybe there's an easy way to make WinSCP consume less resources? I may only guess, but for ex. WinSCP updates local file list in background, so it uses hooks or smth like that, and maybe this is the reason? Personally, I would be fine with the refresh-when-focused tactics that Total Commander applies for years. I noticed the local filelist is updated many times as I work on my scripts (when I save them) but I don't really need it before I really switch to the WinSCP window.

Can background refresh be an option (perhaps on by default)? I think disabling background refresh and enabling refresh on focus would not take much programming.