I'm so sorry IBS is your version of 'long Covid'. That must be so worrying and uncomfortable for you. I don't have much to offer in the way of suggestions except keep to a bland diet as much as you can. Have you tried the Low Fodmap diet? You really need a dietitian to help with that if you can get a referral. Because the low Fodmap diet cuts out a lot of the foods we need.
But it might be easier for you to digest, as might a low fibre diet.
You could definitely help yourself through trialling the low Fodmap diet by taking an A-Z multivitamin and mineral complex each day. That's what I did, and didn't show any signs of deficiencies.
I have IBS-D too, and find very plain foods help me. I more or less live on boiled eggs, fish of all kinds, steamed vegetables, rice, sometimes potatoes, and toast and butter. No sauces, no seasonings except salt, just really plain food.
I'm not sure if my IBS was connected to Covid or not. I got a slight upset tummy in 2018 but it only lasted a week then I was okay. But about 3 weeks before I came down with Covid in April 2020, that was when my IBS really started. So I will never know if it was connected to Covid or not.