Wow, those are some really nice quality plots! I’d say your sequencing run went very well.
Which is really good since the V3-V4 region is fairly long and can be hard to hit (depending on your specific primers I think you only have about ~90 bases free after 2x300 sequencing for that region).
Your forward reads are excellent, I would probably keep the entire length or trim at ~280 (use
trunc-len of 0 to skip truncation in that direction).
You reverse is also great, I would probably trim around ~270, but you have enough wiggle room that you could trim a little closer like ~240 if you kep the full length on the forward reads.
Then see if you get good merging from your denoising stats. Ideally you won’t see much/any drop-off at that point, but let us know if the counts before/after merging don’t look good.