Woke up to weird sound. Fragile, DDOS attack and remote access all in my AX6000 router log.

For slowdowns, that needs to be investigated, for example, when it happens, is it slow for wired devices as well as wireless?

Usuallly it is impossible for a router to do much about DOS attack, since the purpose of one is not to attack the router itself (with the exception of extremely rare cases such as devices with remote access enabled and unsecured), but instead to saturate the last mile of your WAN connection, and fill any buffers as rapidly as possible so all legit traffic gets dropped. For example, a user has a 100mbit connection, but they are hit with a DDOS at 10+Gbps, only 100Mbps of junk will make it through the last mile, but somewhere within the ISPs network, the excess traffic will start getting dropped as buffers filll, and the user's connection becomes useless during the attack. It is uncommon for it to ever happen to a home user, with the exception of some toxic gaming communities where if they can ge ta hold of someone's WAN IP they may do a DOS attack during a match, or if they find that the user is on comcast or some other ISP with a data cap, they will do a DOS attack over night as a way of burning through their data cap since ISPs like comcast and many other capped ones log traffic based on what is directed towards your WAN IP regardless of what reaches you, thus someone can have a 200mbit connection, but a 10Gbps DOS attack will eat through their cap at 10Gbps even though only a tiny fraction of that data will actually reach the user.

Overall for home users, that is about as bas as a DOS attack will get.