What I ran in my Linksys WRT54G was DD-WRT, it provided all the normal functionality sans the occasional lockups the stock firmware did, and in addition you could attach to other networks, you could participate in a mesh network, you could increase the transmitter power from 7mw up to as much as 100mw (and this really helped in my environment).

I assume you’ve already checked your model on the Supported Devices table?

There are so many variations of the WRT54G that it may be difficult for someone to answer the question.

FreshTomato still supports these devices.

Unfortunately no, not for a serious use case. Not only the RAM & storage, the CPU & networking chipset themselves are insufficient for modern security, not with reasonable performance, at least.

Crazy and I thought 2GB RAM in a Turris Omnia are low XD

Good luck!

Bro, resolder ram and rom, i recently upgraded spi chip in my xiaomi 4a to 32 megabytes or 256 megabits if i have to be precise and it’s working fine in my apartment right now, but remember, most devices still have troubles with wpa3 security protocol, also remember to turn off option “dissociate on low acknowledgment” because your devices gonna be reconnecting constantly because of these options, also ram upgradable too, but difficulty is higher, i upgraded ram to 64 megabytes and flash to 32 megabytes in my tplink wr740n recently, flash upgrade is doing good, but ram not so good even though on openwrt wiki there’s mentioned that d43 64 megabytes ram chips should work just fine, but I’m working through it, also i have tplink wr841n and dlink dir 300 and dir 615 to upgrade, then i have to try to port firmware to my another netis router, so far it’s easy to compile what was already ported, problem arise when you have to adapt drivers or unsupported architectures, for example, i have compiler for dlink and netis available but they were not ported into openwrt yet so i will have to do it myself