While I hate relegating perfectly usable Android phones to a landfill, identity theft also sucks. The bottom line is that manufacturers should be required to supply updates for longer periods of time or provide a means to completely unlock them for free and let end users install new versions of the ROM.

Perhaps images, video, font etc. rendering could be compromised?

Yes, it already happen in the past. Also the Wi-Fi and Bluetooth stack got exploited, like multiple kernel drivers.

But it shouldn't be a matter of "in the past was X exploited?" but more on having a correct security posture.

Honestly if you are arguing about wasting a "perfectly working phone" you should blame it on the vendor, especially Android devices vendors have this let's say "defect" of dropping the support after 4/5 years.

Also not going to talk about custom ROMs (with the super rare exclusion of some) managed by god knows who, without any security team behind.

Since even the NFC and Cellular Network stack got vulnerabilities the only way you would consider an old phone "safe" to use is just turning it into the equivalent of a local ARM server.

Also pretty fun seeing the replies in the original post talking about how Google Play store shouldn't have malware on it.

Nowadays people rarely attack individual random users. I believe the risk of running outdated software is super inflated and mediatic, 99% of people would be absolutely fine running a version of Android from 3 years ago or Windows 8.