It's quite possible. I use an old HP 24UH 60Hz 1080p display as a secondary with an Acer XF270HU 144Hz 1440p display as primary, running on a 2070 with a Ryzen 7 3700X. Playing videos on my secondary does limit the refresh rate/framerate on my primary (noticeably worse frame/refresh rate when dragging windows, and playing videos on both monitors is sometimes troublesome, especially if the 144Hz monitor was displaying video first). That being said, playing video on the secondary monitor doesn't really cap refresh rate or frame rate when playing games, and I assume it won't interfere with any fullscreen application. But you may have different results. Best thing you can do is try it, and if you don't like the results, then just get rid of the old monitor.