LostDog99

Did you run your world through a program similar to WorldEdit recently? Programs like that have a tendency to erase all existing mobs after having been run through the program.

It's possible the issue could be related to the shaders you're using. Does this occur when you do not have any shaders installed? 

Being unable to look around with the mousepad, while moving with keyboard controls is likely an issue with your mouse settings on your computer.

(If a mod is lurking, MC-275053 and MC-275052 are the same issue and could be condensed into one report.)

Unable to reproduce the described issue in 1.21.1 Java and Bedrock versions. The duplication rail in the screenshot pushes the block behind it breaking the redstone dust above it and the rail.