Stuck on a plateau for 3+ months every lift has stalled or regressed

[SuspectAscend]

I've been lifting consistently and I'm stuck on a plateau that's been going on since around March. I'm maintaining my body weight (not bulking or cutting cus i'd lose more muscle and i don't wanna get fat), protein (130g), sleep(8-9 hrs) and recovery are in check, and I train each muscle group twice a week with about 12 hard sets per week. I do 2 working sets per exercise and usually train to failure. My biggest issue is that my lifts aren't progressing at all. For example, my shoulder press machine used to be 56 kg for 8 reps, but now I'm struggling with 49 kg for 6 clean reps. If I try to get a 7th rep, my back comes off the pad and my form breaks down, so I stop there. Chest strength has dropped a bit too, while back and arms have stayed about the same. I rest around 3 minutes between sets. Has anyone experienced this? Would you recommend changing proximity to failure, adding a deload, adjusting volume, or using a different progression method? I'm looking for evidence-based advice rather than just "bulk."

Split:

Monday: rest
Tuesday: chest bicep
Wednesday: Back and tricep
Thursday: Shoulders
Friday: Rest
Saturday: Chest and Arms
Sunday: Back and Shoulders

I seriously don't know what to do I finished a pretty aggressive cut earlier this year, going from 92.5 kg in January to around 70 kg by March (over 20 kg lost). I'm now maintaining my weight and trying to focus on building muscle and strength, but since March my lifts have either stalled or regressed despite consistency.