The supply isn't going to be increased to the point it will loose its value, instead of all of it is finally mined completely, then there's going to be a limitation of supply as it's been reduced after every halving, at that point value is even going to be higher as there will be limited supply in the market, only when the supply is above demand value drops but in the reverse value does increases.
To be able to mine everything still takes a long time, Bitcoin will be completed in the mine in 2140 or about 118 years from now. Of course, we will not be in that year and only our generation can know it.
Right now, the circulating supply is still 19.77 Million BTC, there is still 1.23 Million BTC left.
If they are worried about the future of Bitcoin, they have not understood how Bitcoin has grown to date.
Some of the circulating BTC supply will also not move at all, assuming that the wallet with BTC does not move due to the loss of the seed key or the wallet left by the owner due to death and so on, it will be BTC that does not move so that the actual circulating supply is less than 21 million BTC, Of course this will make Bitcoin even rarer in the future.