Thanks, Patrick. I'm using an X-windows display from RHEL Linux 7.2 back to Windows 10. Here's the Help->About output from SlickEdit running on Linux (I've trimmed some output that my employer might consider sensitive):
SlickEdit Pro 2020 (v25.0.2.0 64-bit)
OS: Linux
OS Version: Red Hat Enterprise Linux Server release 7.2 (Maipo)
Kernel Level: 3.10.0-327.el7.x86_64
Build Version: #1 SMP Thu Oct 29 17:29:29 EDT 2015
Processor Architecture: x86_64
X Server Vendor: Colin Harrison
Window Manager: Unknown
Display manager: /usr/sbin/gdm
Memory: 83% Load, 205226MB/245036MB Virtual
Shell Information: /apps/linux/slickedit/x86_64/v25/bin/secsh -i
Screen Size: 3840 x 1208
Project Type: Single file project - Other
Language: .h (C/C++)
Encoding: ACP (30001)
Installation Directory: /apps/linux/slickedit/x86_64/v25/
Configuration Directory: /home/bbaum/.slickedit/25.0.2/
Migrated from: /home/bbaum/.slickedit/24.0.2/
--------------------------------------------------------------------
OS Info (From /etc/os-release):
NAME="Red Hat Enterprise Linux Server"
VERSION="7.2 (Maipo)"
ID="rhel"
ID_LIKE="fedora"
VERSION_ID="7.2"
PRETTY_NAME="Red Hat Enterprise Linux Server 7.2 (Maipo)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:redhat:enterprise_linux:7.2:GA:server"
HOME_URL="https://www.redhat.com/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Red Hat Enterprise Linux 7"
REDHAT_BUGZILLA_PRODUCT_VERSION=7.2
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="7.2"
As far as $XDG_SESSION_TYPE output, it seems XDG_SESSION_TYPE isn't in my list of env variables, although XDG_SESSION_ID and SDG_RUNTIME_DIR are (?), so running $XDG_SESSION_TYPE as a command produced no output.
For what it's worth, I also have SlickEdit v25.0.2.0 running natively on Windows 10 but I don't have the same issue when running SE on Windows -- pressing Ctrl+Shift+F pops up the Find-in-Files dialog and focus immediately moves to that dialog.
Finally, I was unable to locate any settings (Windows or Linux) related to "focus follows mouse". Patrick's explanation made sense and I have seen that setting when I log in natively to Linux. However, in this environment I use PuTTY to ssh into a Linux box, and X-Display (XMing) back to Windows. I'll snoop around in the XMing settings to see if there's something that stands out.