I would look at a few things in relation to your new router. Routers often auto-select the best WiFi channel on startup, but that is not always ideal. I would maybe select your own ‘fixed’ WiFi channels, best if they are non-overlapping channels such as 1, 6 or 11. Maybe start with channel 1 for the 2.4ghz band and set a channel-width of 20MHz.

If you still encounter issues, then try channel 6 or 11. Give each channel an hour or two before moving onto trying the next one.

If all three 2.4ghz channels do not bring about success, then try cabling a single Sonos device to the network - its best to choose a ‘modern’ (standalone) device, such as a Sonos One for example, which is likely to have a better built-in WiFi card compared to an older Sonos product, but stick to the older product if that suits best for your setup. It’s better though if it’s standalone and not part of a stereo pair etc.

When wiring a Sonos product to the router, try to do that direct, rather than through a network switch and keep the device away from the router itself - the further, the better.

The effect of cabling a sonos device, means your entire system will switchover to SonosNet where the devices use their internal wireless connection like a WiFi mesh system. This document explains a little more about that feature:

https://support.sonos.com/s/article/3235

When running your devices on SonosNet, goto ‘Settings/System/Network’ and set the SonosNet channel so that it is at least 5 channels away from your routers 2.4ghz channel. So if your router is set to channel 1. for example, then set the SonosNet channel to either 6 or 11 to prevent interference.

In regards to ‘general’ WiFi interference about your home, you may also find this Sonos support document and video helpful too:

https://support.sonos.com/s/article/3286

https://youtu.be/3fQAAL5IwTE