UK and US banks absolutely do have reserve requirements and they are neither 1% nor 0%. I have no idea where you're getting that from. The reserve requirements vary by type of bank and type and risk weighting of asset.
Here is the documentation that explains the capital requirements for a regulated entity (not just banks, but including banks) in the UK
Reserve requirements are capital requirements. "reserve" here is capital that you reserve to withstand losses in particular classes of assets.
There are also requirements for particular proportions of the capital base to be held in liquid assets (cash and near cash) in order to pay back deposits etc.
Banks still have capitalization requirements that are required to supply money for withdrawals, and those have (for several decades, I believe) been far more stringent than the reserve requirements. Reserve requirements are the amount of cash they need to hold specifically in the central bank, whereas capital requirements are a more general notion of cash.
No, they don't. In the event of a bank run, a bank cannot cover their liabilities. This is the same thing that you point in tether as a fatal flaw and a "scam".
Timing difference, i.e. majority of assets are not held in cash (it is put to work), so if many people try to withdraw lots of money at the same time, it can trigger a downward spiral (“bank run”).
I don't understand, what does that have to do with anything? The issue being discussed is Tether, and how it's totally a pyramid scam since it doesn't hold 100% in reserve.
Here is the documentation that explains the capital requirements for a regulated entity (not just banks, but including banks) in the UK
https://www.handbook.fca.org.uk/handbook/glossary/G1567.html