If you set criteria for opening a position using a formulaic expression, you can use the TICKER function to backtest on a custom list of tickers, for example:

ticker(aapl, meta, msft) and "the rest of your formula goes here"

However, if this is a massive list of tickers, you need first to create a watchlist and then specify the watchlist's name in the formula as the stock universe:

[your_watch_list_name] and "the rest of your formula goes here"

It is also worth noting that symbols on the watchlist or symbols written in the TICKER function can be any supported symbols: stocks, currency pairs, cryptocurrencies, etc.