Actuary/comp science OR comp sci/applied mathematics
If you wanna become an actuary then that's a good double degree since some Excel processes can most likely be more efficient with the use of Python. However if you wanna pursue a software dev role, I think actuary doesn't really help much. All I learnt in uni was relating to Excel (barely), statistics, risk/insurance, which you'll probably learn better in applied maths if you wanted to use it in combination with computer science.
If I could restart I'd do comp sci rather than actuary because of the fact that knowing coding has a lot more potential for huge salary/creating your own projects. Actuary is more of a linear path from what I know. You basically do 3 years of uni to finish part 1 qualification, then do part 2s with uni+the institute for a pay rise, then part 3s with the institute for another pay rise. The part 2s and 3s are usually done while working which makes it pretty hard.
The only issue I see with pursuing actuarial is that payrises and promotions are sorta limited to these exams, so you're time gated. Like if you wanna become a senior actuary or a manager or something you probably need part 3s most of the time. But with comp sci, if you're very good you can just get promoted/get better roles really quickly since there's no exams time gating you, but more of your skill instead.
But yea you can't go wrong with either option tbh, but I'd only do the actuary double if you actually want to become an actuary. If you know you're set on pursuing the comp sci field, the actuary double is mostly useless in my opinion.