

Q1: What does "isn't affected by ... effects" mean, exactly?
This effect prevents Digimon from being affected by effects. For example, your Digmon won't suspend if it's chosen for a "suspend 1 of your opponent's Digimon" effect, and its DP won't be reduced if it's chosen for a "1 of your opponent's Digimon gets -3000 DP" effect.
Q2: Can a card that has an "isn't affected by ... effects" effect be chosen for an effect?
Yes, it can be chosen.
Q3: Can a card that has an "isn't affected by ... effects" effect be given an effect?
Yes, it can. However, it won't be affected by it.
Q6: A card that has an "isn't affected by ... effects" effect was given an effect that triggers at a timing such as When Attacking. Will the effect trigger if that card later meets the trigger conditions?
If the Digimon isn't affected by effects upon the trigger timing, the effect won't trigger.
Lv.6 Gankoomon (X Antibody) BT20-059 R Mega | Data | Holy Warrior/X Antibody/Royal Knight [When Digivolving] <De-Digivolve 2> 1 of your opponent's Digimon. Then, if [Gankoomon] or [X Antibody] is in this Digimon's digivolution cards, until the end of your opponent's turn, none of your Digimon are affected by your opponent's Digimon's effects. [Opponent's Turn] All of your Digimon with [Sistermon] or [Huckmon] in their names or the [Royal Knight] trait gain <Reboot> and <Blocker>. --- [Opponent's Turn] While this Digimon is [Jesmon GX], all of your Digimon gain <Reboot> and <Blocker>.
Lv.6 Gankoomon (X Antibody) BT20-059 R Mega | Data | Holy Warrior/X Antibody/Royal Knight [Digivolve] [Gankoomon]: Cost 2 [When Digivolving] <De-Digivolve 2> 1 of your opponent's Digimon. Then, if [Gankoomon] or [X Antibody] is in this Digimon's digivolution cards, until the end of your opponent's turn, none of your Digimon are affected by your opponent's Digimon's effects. [Opponent's Turn] All of your Digimon with [Sistermon] or [Huckmon] in their names or the [Royal Knight] trait gain <Reboot> and <Blocker>. --- [Opponent's Turn] While this Digimon is [Jesmon GX], all of your Digimon gain <Reboot> and <Blocker>.
Lv.6 Gankoomon (X Antibody) BT20-059 R mega | Data | Holy Warrior/X Antibody/Royal Knight [Digivolve] [Gankoomon]: Cost 2 [When Digivolving] <De-Digivolve 2> 1 of your opponent's Digimon. Then, if [Gankoomon] or [X Antibody] is in this Digimon's digivolution cards, until the end of your opponent's turn, none of your Digimon are affected by your opponent's Digimon's effects. [Opponent's Turn] All of your Digimon with [Sistermon] or [Huckmon] in their names or the [Royal Knight] trait gain <Reboot> and <Blocker>. --- [Opponent's Turn] While this Digimon is [Jesmon GX] all of your Digimon gain <Reboot> and <Blocker>.
Lv.6 ガンクゥモンX抗体 BT20-059 R 究極体 | データ種 | 聖騎士型/X抗体/ロイヤルナイツ 【進化時】相手のデジモン1体を≪退化2≫。その後、このデジモンの進化元に「ガンクゥモン」/「X抗体」があるなら、相手のターン終了まで、自分のデジモン全ては相手のデジモンの効果を受けない。 【相手のターン】名称に「シスタモン」/「ハックモン」を含むか特徴に「ロイヤルナイツ」を持つ自分のデジモン全ては≪再起動≫と≪ブロッカー≫を得る。 --- 【相手のターン】このデジモンが「ジエスモンGX」の間、自分のデジモン全ては≪再起動≫と≪ブロッカー≫を得る。