What to watch is down to personal taste. What I would do once you are in the UK (I think iPlayer is blocked abroad) is go to iPlayer website
https://www.bbc.co.uk/iplayer and then click on Categories and choose one of interest.
Once on the Category page (Science and Engineering shown above - just the top part) the order is the BBC's choice - i.e. what they want to promote) , Alternatively click on Featured and change to Most Recent or A-Z. Some programs are only available for x days (used to be 90 days I think) but others can be from 20 years or more ago.
Alternatively, use the search box to type in a topic of interest.
Alternatively, Channels shows the programs according to the BBC terrestrial channels. BBC 1 is light entertainment for the masses
, BBC is less mainstream, BBC 3 I can't say as never watch it! and BBC 4 is meant to be a bit more serious but I find it too light now. Long gone are the days of serious documentaries - now they are all rapid camera shots, booming sound effects and GCI
Note that due to copyright, iPlayer tends to show only the BBC's own content. I will rarely show content made by others (e.g. films).