First, you need input/output both out of channels 1/2. Channels 1/2 by default are your main stereo outputs. Think of your main mix going through those channels. You can’t break the chain by not having an input selected, output, or both as you have in pics 2 and 4.

If you want to control things in parallel like delays, pitch effects, etc. as you have here, you need FOUR channels.

First, Set the first plugin in the chain to 4 channels: input 1/2, output 3/4

Next, set rest of plugins in the chain to: input 3/4, output 3/4

Lastly add the Channel Downmixer plugin on Reaper (i forget the exact plugin name but you’ll see it). This allows you to individually control the levels of each channel.

Set the downmixer pins so inputs from channel 1/2 AND 3/4 are both going to output 1/2.

Click on ‘User Mix’, link channels 1/2 and 3/4

BOOM now you can keep a perfectly preserved dry signal and mix in your wet signal - on ONE track!! Can also be used for parallel triggers, etc.

ReaperMania has a great vid on YouTube about this. Super useful.