Your basic understanding is correct:

• In 5th āra (Duḥṣam / Pañcam kāl) of Bhārata-kṣetra, no new soul can attain moksha.
• Yet we say Bhagvān Mahāvīr and Gaṇadhar Gautam Swami lived “in our current time-cycle (avasarpiṇī)” and attained moksha near what we call “now”.

The confusion comes from mixing up:

• Which half-cycle? – current avasarpiṇī (downward cycle)

with

• Which āra (era) inside that half-cycle?

1. In which āra did Gautam Swami attain moksha?

According to Jain tradition:

• Mahāvīr Bhagvān and his Gaṇadhars (including Gautam Swami) lived in the 4th āra of the current avasarpiṇī, called Duḥṣamā–Suṣamā.
• Keval-jñān and moksha are possible only in the 3rd and 4th āra of a half-cycle in Bhārata-kṣetra.
• Therefore, Gautam Swami’s moksha is in the 4th āra, not the 5th.

Mahāvīr’s nirvāṇa and the liberation of his disciples (including Gautam Swami and later Jambu Swami, who is accepted as the last liberated soul from Bhārata-kṣetra in this avasarpiṇī) all happen before the 5th āra actually begins.

2. Then why do some people say “in 5th āra / Pañcam kāl”?

Common reasons people say this:

1. They mean “in our current time-cycle (avasarpiṇī)”, not strictly “in the 5th āra”.
2. They know we are now in the 5th āra, so they loosely talk as if everything close to our time is “5th kāl”, even though, scripturally, Mahāvīr and his Gaṇadhars belong to the end of the 4th āra.

From the doctrinal (śāstriya) point of view:

• Now we are in 5th āra (Duḥṣam kāl) → no Tirthankars, no Kevalis, no moksha from Bhārata-kṣetra.
• Before this, at the very end of 4th āra, Mahāvīr Bhagvān, Gautam Swami, Sudharmā Swami, Jambu Swami etc. attained keval-jñān and moksha.

So:

• Statement: “Gautam Swami attained moksha in 5th āra” → not correct according to Jain time theory.
• Correct understanding:

- Same avasarpiṇī half-cycle as now, - But different āra – 4th (Duḥṣamā–Suṣamā); - After them, 5th āra started, and from then on moksha from Bhārata-kṣetra is not possible.