If you are using the Manager it shows what is the current version and recommended version when you select the application you want to patch.

You can always check this post! There's a link to the most recent YT apk from APKPure.

Here's the link: https://m.apkpure.com/youtube/com.google.android.youtube/download; using this version is unlikely to give you any issues.

The recommended version is v18.23.35 though. The link for that APK is here: https://apkpure.com/youtube/com.google.android.youtube/variant/18.23.35-XAPK.

Also, you can always check the suggested version in the patcher:

Does ReVanced App work on iOS devices?