@Bow I've also struggled with this. First off, I'm sorry that you feel ashamed, there is nothing to be ashamed off, the people on Tic Tok are being judgemental and clearly don't understand mental health issues. I think it would be valuable for you to learn to have compassion for yourself rather than shame. I understand this can be difficult. And I know someone who has gone over six months without a shower. You are NOT alone in this struggle.
During a mental health crisis, personal hygiene goes out the window for me. The best I can realistically hope for is to get into the bathroom and change clothes every few days, with at attempt to step into the shower (which may not lead to actually getting clean). I've had issues with fungal skin infections because of this: if this ever happens to you, there are over the counter skin treatments that can fix this. The idea of fungal infections sound yuk, but I've always been able to easily treat them once the mental health crisis is over.
Even when I'm out of crisis mode, I still find it hard to shower every day, so I aim for every second day. I find having a routine and an alarm set can be helpful. Showering is literally always on my to do list for the day, sometimes it gets done and sometimes it doesn't. Clean underwear and putting deodorant on twice a day can help reduce the need to shower.
Here is an app I use to help with my executive function. This lists some good suggestions both to help you shower and what to do when showering gets too much: I need another solution
Executive functioning issues are what causes this struggle. It may help you to research executive functioning so that you understand this better. You can find a lot on You Tube by content creators who struggle with personal hygiene due to executive dysfunction. This is a common issue with: ADHD, autism, depression, C-PTSD and schizophrenia, so it can help to look for content made by people with these disabilities/conditions. NOT saying you have one or more of these things, just that you should find the executive dysfunction struggles relatable. Please see a clinical psychologist or a psychiatrist if you want to get assessed for any diagnosis.