No lawful line of succession for the UK monarchy since 1919 means there’s no King or Queen in/of Canada or the UK

The Bill of Rights 1689 and the Act of Settlement 1701 restricts succession to the UK throne to the legitimate Protestant descendants of Sophia of Hanover (Germany’s House of Hanover monarchy) who are in “communion with the Church of England”

However, during World War I the Titles Deprivation Act of 1917 stripped the “House of Hanover” of their titles of nobility in the UK. In 1918 Ernst August was forced to abdicate in the course of the November Revolution, and the new Weimar Republic then abolished all German titles of nobility, including those of the House of Hanover.

In August 1919, at the beginning of the Weimar Republic (1919–1933), Germany’s first democratic constitution officially abolished royalty and nobility, and the respective legal privileges and immunities appertaining to an individual, a family or any heirs. All German nobility as a legally defined class were forever abolished including the UK’s German Saxe-Coburg & Gotha monarchy and Germany’s House of Hanover – the monarchy that all UK monarchies derive their legitimacy from.

Article 109: All Germans are equal before the law. Men and women have the same fundamental civil rights and duties. Public legal privileges or disadvantages of birth or of rank are abolished. Titles of nobility shall be regarded merely as part of the name and may no longer be bestowed. Titles may only be bestowed when they indicate an office or profession; academic degrees are not affected hereby. Orders and decorations shall not be conferred by the state. No German shall accept titles or orders from a foreign government.

Abolish means to end the observance or effect of (something, such as a law) : to completely do away with (something) : annul (to declare or make legally invalid or void)

If someone in authority abolishes a system or practice, they formally put an end to it.

Academic Law Dictionary:

abolish: verb abate, abolere, abrogate, annihilate, annul, cancel, declare null and void, delere, delete, deprive of force, destroy, disannul, discontinue, disestablish, dispense with, dispose, dissolve, eliminate, eradicate, exstinguere, exterminate, extinguish, extirpate, invalidate, negate, nullify, obliterate, override, overrule, overturn, prohibit, quash, raze, render null and void, …

Collins dictionary of law. W. J. Stewart. 2001


to terminate the legal effect of some provision or doctrine.
In law, void means of no legal effect. An action, document or transaction which is void is of no legal effect whatsoever: an absolute nullity — the law treats it as if it had never existed or happened.
That means there is no lawful line of succession. Lawful line of succession ended when the UK’s German Saxe-Coburg & Gotha and Germany’s House of Hanover monarchies were both forever abolished (made legally invalid or void) in 1919.