The 1000 nits brightness seems to be for XDR (extended dynamic range) content, such as movies. I'm not sure that you are getting more than 500 nits for most of the things (chat, email, stocks) that you are currently doing.
Note that the M4 MacBook Air has a more limited set of ports than any of the 14" M1 {Pro/Max} MacBook Pros – no third USB-C / Thunderbolt port, no HDMI port, no SDXC card slot.