Never had time to wrap my head around forks. If I have a wallet from the time before forks existed, do I have to do anything to not lose my money in case a fork "wins"? Or is this the wrong way to think about forks?
I personally would only import that wallet.dat on a fully offline/airgapped computer (which you've synched to the BTC blockchain first), prepare the transaction to move those coins to a safe address (like an hardware wallet), put that transaction on a USB stick, put that stick in an online computer and broadcast the transaction.
But first and foremost: buy a hardware wallet, learn how it works, make sure to have copies of the seed (24 words probably), "warm" you address by having a friend send you 0.01 BTC on it or something, move these coins to another address (you really want to be sure this address works and everything is smooth). This costs some money (a hardware wallet + the fees to "warm up" the addresses / test how it all works) but if you have an old wallet.dat with some or a lot of BTCs, it's worth it.
And also: move the most valuable coins first. So BTC first, then BCH, then BSV. I'm not kidding with this. So many scams with the forks / executables to synch the forks etc. Don't even think about moving the BCH/BSV etc. before having moved all the BTCs.
Re- forks: depends on what you mean by "winning". BTC "won" over BCH if you take the market price (45 K vs 500 USD) but BCH lives on. So if your wallet.dat predates that fork, you'll have both. Once again: do not ever try to move the BCH before moving the BTC... For you want to minimize the places where you import that wallet.dat for the most important coin.
Now if by "winning" you mean: one chain wins and the fork dies a sad death, the point is moot as there's no other fork/chain and hence coins there are worth 0.
If you have an old wallet.dat, you'll have coins on the BTC chain, the BCH chain, the BSV chain, the BTG Gold chain, etc.
If you purchase a hardware wallet, make sure you buy it directly from the company making them, and read the official instructions.
There have been scams where people sell hardware wallets with seeds that the scammers provided, and once the victim uses the hardware wallet with the scammer-provided seed, the scammer steals the victim's coins.
