Why do you say the RX550 is not UEFI compatible?
Greetings,
I don't know if it is or isn't. Older cards are sometimes non compliant and require CSM for boot. Some older cards also had BIOS updates that improved compatibility or performance.
Its still not clear why your system is beeping 4 times at boot.
I don't follow AMD cards any longer. I started using nVidia based cards and today (EVGA) exclusively about 15 years. AMD cards are great, but there were almost always some kind of driver issue, etc and I got tired of both AMD CPU's and ATi now (AMD) based video cards.
I chased the whole performance, AMD overclocking thing, priding myself on saving money and having a overclocked system with a slower CPU that performed as well or better in some cases than an higher rated intel based system. As time passed, I stopped having the time on weekends to search and test for the right memory settings, FSB, multiplier, etc so my system would run fast, but more importantly stable. Today, stability is the most important thing for me. For people that have the time, AMD based systems are great. Ryzen is a good platform. I just prefer intel, the same way i prefer windows over MAC.