You have a device with 4MB flash and/or 32MB RAM.
You have read and understood the 4/32 warning.
You have adjusted your expectations according to this warning.
You still want to install OpenWrt on your 4/32 device for
Now you are asking: What can I do?
Find answers below.
This page also applies to 8 MB flash devices, as they will have problems installing more than the basic set of packages.
For 8 MB devices, “surgery” to remove PPP, IPv6, or similar is probably not needed, but concept of building or assembling your own, custom image to save space is applicable.
See also Security
Chose the OpenWrt version according to your needs for maintenance releases and security fixes.
What can I do against the 4/8 MB flash issue?
Why should I build my own image rather than installing packages?
Building your own image compresses the packages you need to about half the size compared to installing them after you flash.
What can I do against the 32 and 64 MB RAM issue?
4/32 devices can be used with the latest versions mostly OK, provided that only basic routing functions are used.
I am using three of these devices: MR3040v2, tl-841v9 and tl-1043ndv1 on 19.07 build.
You're definitely looking at a custom build, but it can work for basic stuff. This is simpler than using extroot, which has the problem that the filesystem driver etc still must be in internal flash. Also its kind of pointless to have a bunch of large packages (VPN, etc.) stored in extroot but no RAM to run them on.