I machine appliqué a lot. I also use invisible thread a lot. I use regular thread in my bobbin in a neutral color. I use Heat n Bond lite as my fusible, haven’t had a lot of luck with steam a seam.
sometimes using a lightweight stabilizer on the back helps - especially if the background fabric is very lightweight. I Always use a blanket stitch to stitch appliqués. The straight horizontal stitch laying just outside along the edges of the appliqué, the ( bites going in about an 1/8”. Zigzags always cause fraying and I am not a fan of satin stitch at all. A small blanket stitch is pretty much invisible on the finished pieces.