Yes, we do can have a program in such format. But it would be more like a 'Scanner' than a general 'Screener'. i.e. the program will be able to 'scan' for valid signals on different 'symbols charts data'.

Yes, you can use the scanner format program to work with any of the symbols available on Tradingview platform.

No, unfortunately, you won't be able to connect the scanner format pinescript program to your watchlists. You'll have to define/mention the 'required symbols' to be 'scanned for' within the program codings.

the max limit of a single program being able to scan is of 40 symbols. However the final number might change depending on the format of indicator being used or conditional logics of valid signals.

you can use scanner on any of the symbols available on TV, recommended for better performance of scanner program is, in a single program, make sure the symbols used are of a single exchange i.e. wouldn't recommend using the equity symbols and forex and crypto symbols all together combined within a single program specially if the 'open and close' times of their markets are different. coz due to difference in market timings, the program wouldn't be able to detect the data effeciently. so better would be to include all the equity market related symbols in one program and all the forex symbols in another program. if the 'timings of the market' are exactly same for all the symbols (from different category), you can include them in a single program.