Want to Sync Music to iPhone without Updating MacOS

I'm running MacOS Mojave and have an iPhone Xs, software 15.4. Since I updated my phone's software, I have been unable to sync my music to my iTunes library . When I plug in the phone to my iMac, iTunes says I must update my OS or it won't let me connect the phone to iTunes. My phone's OS is up to date, so it seems like telling me I have to update to Catalina, which I DO NOT want to do. (I run a couple of other programs on here that don't work with Catalina.) I have the latest version on iTunes (12.9.5). I followed an earlier post that resolved the problem by updating iTunes. I don't see where there is a later version of iTunes available. Is there anything else I should try?