I need to use an older version but I want to keep my new version of Photoshop

I used NIK software for enhancement of my work.  It became an integral part of my workflow.  Now with the upgrade to Photoshop 2020, the Nik software instantly crashes the program.  I want the newer features of PS2020 but I don't want to pay literally hundreds of dollars for the new Nik Software when the OLD software worked just fine.

I won't ask Adobe if they think it's right to kill the compatiblity to the Nik plugin and then have someone buy it and jack up the price for a quick profit.  I just want to know if I can keep both a copy of CS6 and PS2020.  I experienced zero crashes and freezes under CS6.

I've been a subscriber for years if that means anything.

My thanks to the community for your answers.