Don’t like knots in your project when you knit or crochet? Use the Russian join for a smooth, strong, even way to join yarns. There are more tutorials on you tube.
There are several ways to join yarn. Here’s just one.
I am a very novice crocheter and but these looked easy enough.
This works best on wool yarn. Does not work on acrylics.
One of these surely will fit your needs.