Ubuntu Pro offers extended LTS support for free, but only for gnome.
Would it be safer to install ubuntu 22.04 pro and then install xfce4 there than using a no longer supported Zorin 17 Lite version after July 2027?
What is the best option for very old devices?
When You want expand Update Support, then Ubuntu Pro would be the Option, yes.
Or You look for a different OS with xfce. Debian for Example. Debian 13 uses the LTS Kernel 6.12.
The nvidia card of my old notebook doesn't like most of the Debian based distros (I would have to test pure Debian) and had problems with LM 22 XFCE. I'll surely give Zorin 18 Lite a try then, but I'm looking for other ways which could be an alternative if it doesn't work well.
What for a Driver for Your Card do You need?
390 or nouveau, I usually use nouveau.
When You fine with Nouveau, You would have of Course wider Options to choose from. With the 390 Driver ... it isn't really easy. You could download it directly from the Nvidia Website to have it at Hand and then try to install it on Debian. Because of the 6.12 Kernel, it could fail but when You try it first in Live Mode, it wouldn't be bad.
With Nouveau ... Debian xfce should be worth a Try. Rhino Linux uses xfce as Base for theri Desktop, too. But it is a Rolling Release Model which uses Ubuntu as Base. I'm not sure if it is the right for Your Machine. But You could test it of Course.
Does it have to be xfce? You could try MX-Linux xfce or see if PCLOS xfce meets your needs. I had to downgrade to a GT440 in order to get PCLOS installed as it didn't like my GT1030.
You could also give Trinity (TDE) a try?
Hm, I have never heard of the special desktop unicorn, I'll try both in a live session.
I had installed MX Linux XFCE and Q4OS on that laptop, with both the fans were crying permanently. Trinity isn't my taste from the look. Bodhi had worked well with the fans, but caused freezes.
It must not be XFCE but a lightweight one.
I think PCLOS is also a good option but I would try LXQt if I were you, this DE really made big progress 
I can definitely see that working, especially with an Ubuntu base. My question was whether this extended support also allows you to install a different desktop environment on top of Ubuntu pro, or whether that would compromise the system's security.
E.g. ubuntu 20 or 22 pro with xfce or lxqt
you can also bypass 26.04 Wayland restriction and install X11 over, and so Xfce
https://linuxconfig.org/how-to-install-x11-on-ubuntu-26-04