Inability to spell is related to a lack of comprehension. Learning a foreign language or two will help enormously.

Basically, you are trying to remember the correct letters that go to make the 'word' you want to say without thinking about what that word means.

That might mean that you don't comprehend what that 'word' means.

Break it down into morphemes: eg, encourage = in - heart - thing; understand = below - position; conceptual = with - idea - like; ideological = thought - speak - ness.

Am I making any sense at all?

Oh, that would drive me crazy,too. Does your phone not auto correct, a feature designed by some evil developers to frustrate us older users. Just spell how it occurs to you . This is not grammar school.
Peace, sPINLIESEL

I am slightly dyslexic, in that I never really learnt to spell (the times table was never learnt either it sounded too much like brain washing). I can or could however remember the Ruy Lopez chess opening to 12 moves along with all its most popular variants. Nowadays I write on my computer. Each sentence is followed by my going though all the red lines for spellcheck. The more obsque I resort to my phone for guidance. In short use a laptop or desk computer.

@Freedompath I frequently find the word stuck on the tip of my tongue and it won't release itself. I have also never been very good at spelling and the Google android keyboard/ spell checker leaves a lot to be desired but the keyboard is stable. So simply I use the free dictionary from the Playshop...
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I can flick to it in 2 moves and back in two - less if I use a split screen but prefer full screen display particularly when using a virtual keyboard.

Poor spelling and grammar are not related to our "old peoples brain". I have found that young people and phones produce poor spelling, grammar, etc. If you have a computer you can use a free program called "Grammarly" to keep your posts from looking like those of an illiterate. As for phones, I would not know inasmuch as the only thing I can do with my phone is voice calls.

Spellcheck just gives me sentences that are nothing to do with what I’m saying half the time

I find my spell check to be wrong sometimes on my LG V20 phone.

There are some words on the spell check that even though they are spelled correctly the spell check keeps changing them, especially names.