All sounds perfectly normal to me
Poo does change with solids and it is going to get "pooier" like kid/adult poo if your LO is eating solids. Different solids can certainly make a difference but overall yes this is solids poo.
LOs DO strain to poo and it is more difficult with solids poo however this is normal and I was also told by our HV that they need to learn to have a good push to activate all those muscles. You do not want constipation and if this happens you do need to act upon it in a timely manner (prunes yes, or meds if prunes don't do it) however just straining and having a poo face, even the whole body working at it, does not automatically mean constipation.
Constipation will be indicated by straining and no poo coming or small hard pellets. I know you inspect it each nappy change
If it is rock hard it's too hard. If you can form it like play dough it's fine. I loved the well formed poo as I could mould it within the cloth nappy and it just plopped off into the toilet. The stickier poo I had to scrape (we had a poo spoon!) but it is still within the normal range so it's fine.
Do always serve water with solids too. if your LO can't yet use a sippy cup or open cup then you can offer a bottle of water (boiled and allowed to go cold) to ensure he gets the fluid he needs in an easy way. I used both bottle and sippy for a little while until mine could get a decent drink from the sippy cup.
if you do suspect constipation I suggest prunes, the soft ready to eat are without stones and make a nice finger food, just 1 or 2, don't over do it (prob just one for 6 months old). If this doesn't help within the 12-24 hr then another ready to eat prune or even prunes from a can (try to get in fruit juice not syrup so the sugar is only fruit sugar). The canned prunes I discovered were so effective I couldn't give more than 1-2 and not very often at all, mostly I didn't use them. The ready to eat prunes though I used regularly as I kept a gauge on his poo - prune if it was a bit on the hard side and I served carrot if it was a bit too soft. I was able to manage his poo consistency well with those two foods added or avoided on a daily basis.
If however there is no poo coming don't delay on a trip to the doc. You don't want it to become impacted and meds might be needed for a short time.
Formula can certainly have an effect and it takes a little while to adapt to a new formula (even the same brand is different between the powder and the ready to drink I found) but it should be okay - it does sound ok just now.
Hope this puts your mind at rest and helps you feel more prepared