Only the tube is affected by the strike.

Overground, National Rail, DLR, the Elizabeth line, trams and buses are all working. And the few parts of the tube network that don't have any nearby heavy rail services (eg. the Hainault loop on the Central line) are mostly still running.

Sure, the non-tube services are (much!) busier than normal but this situation is actually a great demonstration of one of the most important factors in making public transport useful: route redundancy, so that if one is suspended for whatever reason there are reasonable alternative options for most journeys.