As far as I know athletes or professional players are not allowed to bet on themselves[1]. But as the reference stated, it is somehow in a grey area where some players are able to bet on themselves. According to the regulation, although players are banned on betting on the sports they are involve with, they can bet on other sports that they don't have any affiliation.
Yes and it's also stated in the OP that players can't bet on their own but I think this one can easily be bypassed. Especially if the betting is done only online. We have crypto casinos now which doesn't ask for a KYC. They can also use a VPN and other tools to hide their information more evenly. They can also pay people to place bets for them. Players knows their ability and they can also estimate the ability of their opponents so even if let say no fixing will happen, they still can be tempted to bet.
If I am of the players. I think I will just focus on my career and I don't want to do things which will affect it. Besides, I still can earn and I can earn better once I get popular someday.