Solution to 20A has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
8 Skilful American surgeon starts to operate in theatre (6) ADROIT {A}{DR}{Op...e}{In}{Th...e}
9 Shift and say nothing to intimate friend (5,3) ALTER EGO {ALTER}{EG}{O}
11 Burning daughter's saved by hero struggling with time (3-3) RED-HOT {D} in {HERO}*{T}
12 Sanctions loud speeches after conflict (8) WARRANTS {RANTS}<=>{WAR}
13 Can exercise beginning from dumbbells be repeated (6) LOOPED {LOO}{PE}{Du...s}
20 Drink helping king out (6) ?O?I?N (Addendum - POTION POrTION - See comments)
22 Say, front runners in party helped the US from time to time (8) ATHLETES {pArTy+HeLpEd+ThE+uS}
25 Walks after small breaks (6) SPACES {PACES}<=>{S}
26 Dispose of fish food (8) DUMPLING {DUMP}{LING}
27 King Khan essentially in Jamnagar, after dancing leaves grand function finally (8) MAHARAJA {kHAn} in {JAMnAgAR}*
28 Request going through to obtain seal (6) GASKET {G{ASK}ET}
DOWN
1 After developing Covid, Australia had deported one champion (8) ADVOCATE {COViD+A}*{ATE}
2 Parliamentarian's hugged by that woman - a big mistake! (6) HOWLER {H{OWL}ER}
3 Last to work with current leader (6) STALIN {LAST*}{IN}
5 Surprised that pioneer went ahead (8) STARTLED {START}{LED}
6 Rated in exchange (5-3) TRADE-OFF {RATED}* [RA]
7 Discount offer on gigantic reflecting screens (6) IGNORE [T<=]
15 Actor in a blue mackintosh (8) RAINCOAT*
16 One can't remember when a man is carelessly swallowing ecstasy and cocaine (8) AMNESIAC {A+MAN+IS}* over {E} and {C}
18 Detergent or a bit of soap in clothes basically getting thinner (8) CLEANSER{Cl...s}{LEAN{Soap}ER}
19 Accessory seen in Zurich and Baghdad (7) HANDBAG [T]
21 Frequently poor, possibly has almost nothing, basically! (6) ORPHAN {pOoR}{P}{HAs}{No...g} &lit P/Possibly? (Addendum - {pOoR}{Po...y}{Has}{Al...t}{No...g} - See comments)
23 Recognition in controlling Dadagiri, essentially (6) HOMAGE {HOM{dadAGiri}E}
24 Lines disconnected by Telco's first volunteer (6) ENLIST {LINES*}{Te..o}
Reference List
American = A, Daughter = D, Time = T, Can = LOO, King = R, Exercise = PE, Small = S, Grand = G, Australia = A, Parliamentarian = OWL, Current = IN, Ecstasy = E, Cocaine = C