Theophylact of Ohrid

That is, the change of corruptible creation, which by its very nature is capable of wavering; since it was created, that is, received a beginning of existence, it undoubtedly also has an end. For everything created received a beginning, and therefore, by its very nature, also has an end. And the angels are not infinite by nature; but they received immortality by divine grace. "That which is unshakeable may remain." That is, the future blessings. …

Commentary on Hebrews ↗

Oecumenius

"as of things that are made," that is, those suffering according to nature. For since it takes a beginning and reaches an end, he says, as of things that are made. For since it has been made, and it began from motion, that which comes from non-being to being will reasonably be shaken and moved again in the change. …

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

721. – Then when he says, This phrase, 'Yet once more,' indicates the removal of what is shaken, he explains the words of the prophecy; and he lays great stress on the phrase, Yet once more. For in saying, yet, he shows that they are moveable; but in saying, once more, he indicates that they are to be changed from the state of movability and corruptibility to a state of incorruption and immutability. …

Commentary on Hebrews ↗