For almost seven years now
The AMD AM4 platform still remains relevant, although Ryzen 7000 AM5 versions have been on sale on the market for almost a year now. But AM4 processors still sell in large quantities and, as it turns out, even very old AM4 motherboards still receive BIOS updates.
Reddit users have created a thread discussing this issue. It turned out that many motherboard models based on AMD 300 chipsets still receive new BIOS versions. Some of these boards hit the market over six and a half years ago!
AMD has delivered on its promise. Oldest AM4 motherboards still receive BIOS updates
For comparison: boards based on Intel 300 chipsets, which appeared in 2017, have not been updated since 2021. However, in the case of Intel, this is easily explained: while AMD replaced AM4 with AM5 only a year ago, Intel released LGA 1200 after LGA 1151v2, and now LGA 1700 is relevant.
By the way, at one time AMD promised five years of support for AM4 and, as we see, it more than fulfilled its promise. Moreover, given the success of the Ryzen 5000 and the lack of truly affordable models in the Ryzen 7000 line, it is likely that AM4 support will easily exceed the seven-year mark or more.