Why be concerned with passing Charisma checks at all? The game continues just fine, and you arguably have more interesting results, if you fail every speech check or don't pick one at all.

People are too mind broken by low effort RPGs that focus on dialogue checks.

I had impressive influence on Shadowheart in my first play through using no speech checks at all on her. This made me so compelled by the thought put into the branching writing and the character of Shadowheart that I got through a Shadowheart origin run next just fine with the normal 8 Charisma, no Persuasion, Intimidation, Deception, or Performance proficiency.

You'll still pass some checks if you care to choose them, by virtue of random chance. Even a -1 skill-less, 8 Charisma Shadowheart will pass a 10-check 50% of the time or a 15-check 25% of the time, or even a 30-check 5% of the time (by virtue of 20 success). Hell I didn't even bother to factor in her practically passive Guidance cantrip. So throw out those rolls, especially if you've got advantage (items, cantrips, situational, or reliably through Enhanced Ability, a Bard, Cleric, Druid, and Sorceror level 2 spell) or inspiration to use.

Speaking of proficiency, don't forget that if you want a non-Bard, Paladin, or Warlock to pass speech checks you can invest in skills for proficiency bonus which starts at +2 and reaches +4 by level 9. Equivalent to having 14 to 18 in Charisma, without having picked up that skill. Don't forget you can use a feat to pick up 3 additional skills, or even Actor if you fancy yourself the Deceptive or Performative type. You don't NEED that combat effectiveness - particularly if you're in a twist about passing speech checks for some reason. Actor is easy access to some useful Expertise.

Expertise is of course another layer. A 10 Charisma Rogue with expertise in a speech skill (+8) will outperform a 22-Charisma character without speech skills (+6). Give the 22-Charisma character proficiency (+10), and you'd only need 12 Charisma on that Rogue to match. Not to mention Reliable Talent at level 10 making your rolls, well, very reliable. Consistent 17+ rolls on even an 8 Charisma Rogue without external modifiers.

But really, try to fail some checks sometimes. Or avoid them entirely. You might be surprised.