

Other people’s wifi can affect yours, and vice versa, if they are occupying the same channel(s).
Most likely something on that channel is spamming multicast. That kills most consumer wifi routers (in default settings). Usually something like a sonos or Google home broadcast group.
Could also be a camera that’s constantly transmitting, also occupying the channel for a long time.
But really, it could be anything.
Use an app like PingTools (Android) that can graph what is on each wifi channel. Check to find the cleanest channels in your area and configure your router to use that channel.
Failing that, if it’s on your network and you don’t know what it is…change your Wi-Fi password to kick everything off, then slowly re-add devices with the new password until you find the culprit.
If you’re curious and technically-minded, I highly recommend this write up: https://www.wiisfi.com/
Also, you may be able to get better speeds by using narrower channels. Especially in busy areas. Easier to find 40-80MHz of clean spectrum than it is to find 160MHz. And even easier if you are open to using DFS channels (but these should generally be avoided). Doubling channel-width also doubles the noise, adding 3dB to the bad side of your SNR.
What causes speed drops and packet loss is almost always interference/weak signal. Getting high packet loss on an 80 or 160Mhz channel will be slower than a solid, clean signal on a 40MHz channel.
If you are closing your laptop, don’t. The antennas are usually located in the monitor bezel and are intended to be vertically-oriented, like they would if you were using the laptop. Having it shut means a lot of the signal is directed into the laptop chassis and your desk, which would especially impact upload from the device.

In OpenWRT, I believe it’s in the settings for the “primary” ssid on each radio, which is usually the first one in the list (per radio) on the wireless settings page.
Openwrt also has options to block multicast or convert to unicast. Also make sure you are disabling lower speeds on the radio. That will reduce your max range, but devices that communicate slowly are another killer.
Broadcast and multicast both have to go at the ssid basic rate…the slowest speed supported by the AP. That could be 1Mbps. And then the AP has to repeat it. And depending on the type of traffic, this may also initiate more broadcasts from other devices on the network.
So if you can reduce broadcast/multicast, or increase the minimum speed, you’ll have significantly more time. Since wireless is a shared medium, “time” is really the most critical resource.