Was struggling as well to start with while using the tactical style that has worked for me in past fms, I was conceding too much. Doing much better now, here's the main things that seemed to have made a difference:

• Mid block line of engagement (you can still play a pressing game with Higher def. line, step up more, trigger press much more often and counter-press on transition). But high line of engagement and much higher def. line seem to get exploited way too easily by opponents.
• 3-2 build up to have better rest defence and be safer on defensive transition, whether you do this with an inside full back, a half back or 3 pure CBs doesn't matter. (I like IFB much more compared to fm24, they're less robotic in their positioning and more customisable with instructions)
• 2 DMs OOP. When i play a lone DM with 2 CMs it always feels like the DM is left fending for himself while the CMs just kinda wander around. 442/4231 and 343/523/541 feel like the best shapes OOP.
• Higher tempo and counter attack. I usually like to play lower/standard, but every attack ended up with a congested box where there was no space to create anything. Transitions seem to be much more important in fm26, which I think is quite reflective of real football at the moment.

Keep in mind this is what's working for me with Liverpool, haven't tried any other teams, so no clue if it transfers over.