After the Steam UI update, the too many requests error for your market and inventory access is likely caused by your ISP's use of CGNAT, a technology that shares a single IP address among multiple users. If others on your shared IP make excessive market requests, it can trigger a ban for everyone, which the update may have aggravated. To fix this, contact your ISP to ask for a unique, dedicated public IP address. Alternatively, try using a different connection, like a mobile hotspot, or file another Steam Support ticket specifically mentioning CGNAT issues.