As a person who spends so much time alone, I really miss my grandma as. I haven´t seen her for more than a year, since before the pandemic started.

This sentence was a little long. You can split it like this, and the connection between the two parts is still clear.

When I was a child, my brother and I used to visit her and. I remember that the food she would make always tasted a lot different fromthan my mom's, and then. After eating, we would go out to downtown where my grandpa worked.

Again, I think this sounds more natural broken into multiple sentences. Since this is basically a series of events, it makes sense for each event to have its own sentence. If you had more details to add, then those could go in the same sentence. For example after " I remember that the food ... different than my mom's" you could add a (because) and explain why it tasted different.

He would gaive us free chips every time we went therevisited.

"went there" is a bit generic. (Generally more specific verbs are better in writing.)

Sometimes my grandfatherparents visited our house, which is in a city two hours away from theirs, and that just. Their visits meant a lot of talking and fun, since my mom loved (and still does)s to talk about every member of my family in a way that would makes me laugh so much.

The aside "(and still does)" interrupts flow of the sentence. Since you're talking about something that your mom did in the past, and still does, you can just use present tense.
Alternatively, you can stick to past tense, and most readers will assume that this is something that your mom still loves to do.
"...since my mom loved to talk about every member of my family in a way that would make me laugh so much."

That is something that kept my grandfatherparents entertained for as long as the day went on.