How to go off the radar?

You need to move a country where the tech world hasn’t caught up, very few cameras and the state doesn’t really care about the population enough to even loosely monitor or supervise them. Bribes to help things along still work. But not so wild and dangerous you wouldn’t want to be there. Accessing your money will be tricky, some kind of monthly western union transfer.

I’d say Thailand, Vietnam, or that area.

Travel across America on Greyhound buses, no luggage, no phone, buy new clothes and throw away the old ones every few days, stay in cheap motels, collect pension money from Western Union. To make ends meet I would help small town law enforcement solve murders involving nefarious government agencies and carry out armed raids against the compounds of large scale drug dealers or arms smugglers and steal their money.

How much comfort do you want? You could just sit on the pavement with a bottle of cider asking for change. Many people would actively avoid looking at you.

Providing you didnt need any medical help or get arrested you’d be ok. You’d need to watch out for other homeless people robbing you, drunks beating you up etc.
I’m sure that in a big city, you’d be totally anonymous and off grid. It wouldn’t be my choice of existence, but one that you could do at a moments notice.

If you wanted some sort of luxury, then a prepaid credit card or two would help. Load then up with cash, and provided you could get to mainland europe, you could buy a bike, panniers, tent etc and travel (most of) the world.

You can always just go half way. Go self sufficient for power, heating and water. Dump the phone, TV, internet, let your passport and driving licence lapse. Use cash where possible.

Of course this makes it all the harder to engage with society when needed, health and family reasons.