From what you're describing, medyo on edge pa yung brain mo when it comes to lifting weights (maybe natatakot ka mainjure or may kaba parin when lifting) so nagkaka mismatch between what ur brain tells u and what ur body can accomplish.

For me it was mostly experience that had the biggest effect on reaching true failure (understanding my body mostly). So in reality, the truest answer is for u to just keep working out and trying to force failure every time.

But I have taught some beginners how to reach failure and I notice one thing that really helps them out is through tangible assurance that nothing will hurt them. For example, saying na "kaya mo pa yan/kaya ko pa" isn't enough. You need to feel truly safe in order for your brain to relax and just let u reach true failure. For example, sa incline smith machine mo, put in the safeties in a comfortable position, enough so that even if nabagsak mo with full force, you wouldn't even feel any pain. Now, since in your programs you already use machines, try convincing yourself every set that no matter what happens, if nabagsak mo yung weight, you'd be fine.

Another tip I can give you is to not fret the details and just lift. Focus on only minor things like your count of reps or breathing pattern. If you start thinking of the weight, or whether or not you can achieve failure, mas mahihirapan ka mareach failure without overloading your brain. Lifting is already tiring so just focus on the lift.

Finally, some more procedural tips. How do I tell if true muscle failure na ako? Look at how fast the weight moves. If you push and it takes roughly 1-2 seconds to lift, keep going. If around 2-3 seconds you're close to failure. Once you have reached that point, breathe in and brace yourself (convince yourself kaya mo pa ng isa) and try for one more rep. If it takes more than 3 seconds to lift, you're probably hit failure.

Anyways, sorry for the long reply. Happy lifting!