In the current dnd5e.mjs, Reliable Talent is implemented by setting roll.options.reliableTalent, which then becomes a native min10 modifier on the d20 term via D20Roll.configureModifiers() / D20Die.applyRange().

If we trigger a Reliable Talent relevant roll with disadvantage, it works as intended, and we end up with a formula of 1d20dismin10.

Because of that, a raw d20 term like 1d20dismin10 would be expected to behave the same way and never keep a disadvantaged result below 10.
However, testing shows that 1d20dismin10 can resolve below 10.

Going through the code base, adv/dis are not included in isValidModifier() which establishes which modifiers can be included by the die string serializer

  /**
   * The die modifiers.
   * @type {string}
   */
  get mods() {
    if ( !this.modifiers ) return "";
    return this.modifiers.reduce((acc, mod) => {
      return acc + (dnd5e.utils.isValidDieModifier(mod) ? mod : "");
    }, "");
  }

/**
 * Return whether a string is a valid reroll, explosion, min, or max dice modifier.
 * @param {string} mod      The modifier to test.
 * @returns {boolean}
 */
export function isValidDieModifier(mod) {
  const regex = {
    reroll: /rr?([0-9]+)?([<>=]+)?([0-9]+)?/i,
    explode: /xo?([0-9]+)?([<>=]+)?([0-9]+)?/i,
    minimum: /(?:min)([0-9]+)/i,
    maximum: /(?:max)([0-9]+)/i,
    dropKeep: /[dk]([hl])?([0-9]+)?/i,
    count: /(?:c[sf])([<>=]+)?([0-9]+)?/i
  };
  return Object.values(regex).some(rgx => rgx.test(mod));
}

Instead adv/dis support is added separately in BasicDie.MODIFIERS

/**
 * Add support for system-specific modifiers to the base die.
 */
class BasicDie extends Die {
  /** @inheritDoc */
  static MODIFIERS = {
    ...super.MODIFIERS,
    adv: "advantage",
    dis: "advantage"
  };

This seems to me a bit inconsistent which might also make a modifier-order/evaluation bug plausible.

/r 1d20dismin10 min10 is completely dropped from the modifiers

/r 1d20min10dis

One could still use something like 2d20min10kl and it will work correctly, but on the other hand, not 2d20klmin10 which again drops entirely the min10 from the term modifiers.