How will the BTC mining difficulty level affect validators (btc miners) due to 1/2 reduction in reward after the next halving and possible backlash on general ecosystem?
Halving in mining rewards is predictable and all miners are aware of it. What is not predictable and what significantly affects the profitability of mining is the increase in the difficulty and price of BTC. Investing in mining equipment always involves a bit of gambling.
By the way, mining difficulty has nothing to do with halving. At least not directly. However, halving can have a secondary effect of reducing difficulty, as albert0bsd described.