Welcome to the Eastern Front comrade.

I would suggest:
1. Do not attack in marshes. Go around them, especially regarding the great Prypiat marsh in the middle. It doesn't matter if you have all the bonusses in the world: marshes are gonna wreck your divisions, panzers in particular.
2. 40 withs maybe the meta, but I always feel more comfortable to use 20 width infantry to hold the line and fill the front. They do not de-org like 40 widths do and you can spread them out more efficiently.
3. Use 40 width tanks + 20 width motorized/mechanized to encircle soviets. Again, go around marshes and try to do small encirclements, not the ultra-big ones you see playing against vanilla AI.
4. Expert AI is no joke. The war with USSR can and will be long. Be well prepared from the industrial and equipment side of things, you are going to need everything you have.
5. If you have air superiority use as many bombers as you can to cripple soviet industry and war support. This plays a huge role in softening them up.
You see, you take Moscow and think it's over. Well, it's not.
So bomb the hell out of them or be ready to enjoy a long trip to Vladivostok.

Hope this helps.

The Eastern Front is hell. I have 8000 King Tigers and GW Tigers attached to my infantry just to give them a shot of surviving. ♥♥♥♥♥♥♥ Russians have 1000+ soft attack divisions by 1944. They have 15k-20k aircraft so air superiority is impossible. It's 1945 and yet the Ostfront looks like the Western Front of WWI. I can only do only do 3-month offensives before the attrition forces me to halt.

My only chance of defeating the Soviets is to break their back with a large double pincer, but my 40W Panther divisions are now horribly updated and I'll need to upgrade my Panzerarmees to modern tanks, but that won't be until 1946. Panthers just get cut down like paper targets.

This is gonna be a long war.

es ist fuertig, wir haben keine Chance