Yes but let's imagine a different thing. Let's say you buy a horse in 1996 for $5000. Inflation has meant the purchasing power of that money has halved since then, so to buy a horse of the same value in 2025 you'll need $10k (and you have enough money since wages have increased faster than inflation).
Now let's say you bought the horse in 1996 for $5k and sold it in 2025 for $10k and the government comes along and says you need to pay tax on your $5k profit. You'd say "no, I didn't make a profit, the $10k now has the same purchasing power as the $5k in 1996, I sold it for exactly what I bought it for". But now you're paying 28% tax on your horse that you didn't even make a profit on.
Don't get me wrong, I'm excited to see such a high proposal, I was just days ago saying I didn't think Labour sounded like they wanted a CGT at all, but taxing inflation is likely to be called out by the opposition.