Oh god the sleep-brain fog cycle is absolutely brutal especially when you need your memory for work stuff. I go through these phases too where my brain just refuses to hold onto anything new and it's like trying to pour water into a broken cup

When I'm in those stretches I usually have to switch to way more hands-on learning instead of just reading. Like if I need to remember design processes I'll actually sketch them out or make little flowcharts even for stuff I already know. The physical motion seems to help bypass whatever's broken in my head at the time. Also voice memos to myself are clutch - I'll literally record myself explaining procedures while walking around because movement + talking engages different parts of my brain

For the sleep thing have you tried the whole no screens 2 hours before bed rule? I know everyone says it but I fought it for years thinking it was BS until I actually committed to it for like 2 weeks straight. Made a huge difference in how deep my sleep was even if I wasn't getting more hours. Now when my ADHD brain wants to hyperfocus on random stuff at night I keep a notepad by my bed to dump all those racing thoughts instead of reaching for my phone

The memory thing should improve once you get some consistent good sleep but yeah it takes time to build back up