[3][12][13][14] For the 2021 World Short Course Championships in Abu Dhabi, United Arab Emirates in December, Armstrong entered to compete in the 100 meter backstroke.

[20] Later in the same finals session, Armstrong swam a 44.36 for the backstroke portion of the 4×100 yard medley relay to contribute to a second-place finish in 3:01.44.

[32] He ranked eighth and qualified for the final of the 100 yard backstroke in the prelims heats of the event the following morning, finishing in a time of 44.72 seconds.

[31] In his final individual event, the 100 yard freestyle on the fourth day, he ranked sixteenth in the prelims heats with a 41.92 and qualified for the b-final.

[31] Armstrong swam a personal best time of 48.55 seconds in the 100 meter freestyle on day one of the 2022 US International Team Trials in Greensboro, North Carolina in the preliminary heats, qualifying for the final with an overall sixth-rank.

[38] He lowered his personal best time an additional three-tenths of a second in the final to tie Drew Kibler for fourth-place with a 48.25.

[39] Two days later, he set new Americas, American, and US Open records in the 50 meter backstroke with a time of 24.01 seconds in the prelims heats and advanced to the evening final ranking first.

[44] He won the 100 meter backstroke with a personal best time of 52.20 seconds, qualifying for the World Championships team in the event.

[45] Swimming a personal best time of 22.12 seconds in the 50 meter freestyle morning prelims heats on day five of five, he qualified for the evening final ranking sixth.

[53][54][55] The following day, he split a 52.14 for the backstroke leg of the 4×100 meter mixed medley relay in the final to help win the gold medal with a time of 3:38.79.

[64] On day two, he ranked tenth in the preliminary heats of the 50 meter backstroke with a personal best time of 23.70 seconds, not qualifying for the final.

[68] In the finals of the 100 meter backstroke on day three, he won the b-final with a 53.61, a time which was only slower than the 53.07 swam by a-final winner Daniel Diehl.

[74] He qualified for his first semifinal on day three, ranking eighth in the preliminaries of the 50 meter backstroke with a personal best time of 23.18 seconds.

[77][78][79] Day four, Armstrong started off with a 20.81 on the second leg of the 4×50 meter mixed freestyle relay in the preliminaries, contributing to a total time of 1:29.97 and helping qualify for the final ranking fourth.

[80] Later in the morning, he lost the swim-off against Apostolos Christou of Greece for the last spot in the final of the 50 meter backstroke with a time of 23.30 seconds.

[82] The penultimate morning, he helped qualify the 4×50 meter medley relay for the final in fifth-rank with a backstroke time of 23.34 seconds that contributed to the preliminary mark of 1:32.67.