Most, if not all legacy firmwares are retrievable from the Internet Archive.
This page below, from July 2024, lists 8 releases including the very first one (3.0.0.4.388.31374 from 05/01/2023, your current version) and up to 3.0.0.4.388_33405 (28/05/2024). Then the current Asus website hosts FWs from 3.0.0.4.388_33419 (15/10/2024) onwards.
TUF Gaming AX6000 Dual Band WiFi 6 Gaming Router with dedicated Gaming Port, Dual 2.5G Port, 3steps port forwarding, AiMesh for mesh WiFi, AiProtection Pro network security and AURA RGB lighting.
web.archive.org
Quite a few CVE security vulnerabilities were fixed over 2023 and 2024, you should read the changelogs/release notes
@denis and try and understand whether your current version is vulnerable to a remote attack.
Perhaps you should consider switching to 3.0.0.4.388_33427 (06/11/2024) which is the last known trouble-free version (at least regarding slow page loading over WiFi), with many security uptades contrary to the initial release version that you are currently running (3.0.0.4.388.31374).
I would suggest running at least 3.0.0.4.388_33405 from 28/05/2024, as subsequent updates did not incorporate major security fixes.
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