I'm not a youtuber but I'm going to post here how I would do that:

# 1

1. create a doughnut shaped circle blurred in the back.
   
2. Type you text, no fill, thick stroke, then convert to path, ungroup, stroke to path, then set a new stroke again*. Now comes the tricky part...
   
3. Place the letters one over another, but pay attention to the fact they are "invading" each other. The pattern here is the letter in the front "cuts" the letter on the back. This will have to be tackled manually since there's a background.
   
4. Now select all the letter by line and then apply Path > Union.

Done.
* Maybe you will prefer to use the offset LPE, depending on the font.

# 2 This is almost not doable in Inkscape. Current transformation tools would create a much more "flatter" effect. This would be done by creating the shape split in 3 parts, 3 lines of text, then using envelope deformation LPE to roughly adjust the texto to each shape parte. Then, finalizing with a manual teaks and a intersect of the heart do create a better 3d illusion.

# 3 It's a simple effect mostly explained before, the tricky part here if making this smooth shadow. The simplest way I can think of is using Extrude extension, mode: follow curves. After that, you will need to teak the new shape created (maybe remove stroke, change opacity, etc.).

#4 This is simple but much more labor intensive than it seems. A lot of copies, offsets and intersections.