Does this product keep tile or grout from cracking?

This product is designed for crack suppression for up to 1/8" over a concrete substrate.

Can I use Tavy on shower walls? Do I need an extra waterproofing?

This product is not intended for waterproofing applications. For adequate waterproofing, we recommend Laticrete Hydro Ban or water proof sheet membrane.

Can this product be used on painted concrete block walls? We have a basement shower made of concrete block. It's painted green and I hate the color, but the paint is in perfect condition -- no flaking or peeling. I'd like to update with subway tiles, but have seen that it's not advisable to tile over painted block. Would this work?

The Tavy Thin Skin adhesive can stick to just about any dust-free surface typically found in a home. It will adhere to a painted surface. The wall tile adhesion will ultimately rely on the quality of bond between the current painted surface and concrete block.

Should I be using a non-modified thin set mortar when setting tiles over this product?

You can use either modified or non-modified thinset mortar over Tavy Thin Skin, whichever you prefer.

How long does it take for your Tavy "glue" to dry once the Tavy thin skin is applied? I am going over linoleum.

Tavy instructs to apply the thin-skin directly onto the glue once it has been applied. After installation of thin-skin, you will spread a thin layer of mortar onto the thin-skin. Once the mortar has dried you may begin setting tile.

We have a fairly new raised slab floor (2019) in our laundry room. We are replacing the existing LVP with ceramic tile. Do I need to "seal" the concrete before using the thin skin tile underlayment? If so, what do I use to seal the concrete?

#007 Glue & Thin-Skin Underlayment will work on sealed or unsealed concrete. You do not have to seal it.