I am a lawful permeant resident in USA. Because of the current situation due to COVID-19 and the travel limitations I will be outside USA for more than 6 months from my last exit. Will that have any impact on my next entry to USA or on my record when applying for citizenship?
As far as the documentary requirements for returning to the US, the green card by itself allows you to return to the US after an absence of less than one year. You can always be asked to prove that you maintained residence in the US, no matter how long or short your absence was. (It's possible to be found to have abandoned residence even if each of your absences was less than 6 months.)
There are two impacts that happen at 6 months:
You might break "continuous residence" for naturalization purposes. An absence of between 6 months and 1 year is presumed to break continuous residence unless you provide sufficient evidence of ties to the US to overcome the presumption.
You will be considered an applicant for admission, which means you could be denied entry if you are "inadmissible" under any grounds of inadmissibility. INA 101(a)(13)(C) says that a returning permanent resident is considered to not be seeking admission unless one of several situations applies, including being out of the US for 180 days continuously, having engaged in illegal activity abroad, and a few others. That means that a permanent resident can normally return from a trip of less than 180 days even if they are "inadmissible" (as long as none of the other conditions apply). But if you have been out for more than 180 days, then you need to be careful about any grounds of inadmissibility. This is not usually a problem, as it is uncommon for a permanent resident to be "inadmissible".
However, one ground of inadmissibility that recently changed is the public charge ground of inadmissibility, which became much broader under a new rule that took effect on February 24, 2020. The person's age, health, family status, financial status, and education and skills are all factors considered in the public charge determination now. It is possible that you were admissible when you got your green card under the old rules, but you could be considered to be inadmissible now under the new rules even if your circumstances have not changed. Also, the new rules consider receipt of certain public benefits after February 24, 2020 for more than 12 months out of the last 36 months, to be a heavily-weighted negative factor. This includes some benefits that LPRs may be legally eligible for (including Medicaid which LPRs may be eligible for after 5 years, and SNAP (food stamps) which LPRs may be eligible for after 5 years or after earning 40 quarters of Social Security credits, etc.). So you can be penalized for using benefits that you are legally eligible for, if you subsequently leave the US for more than 180 days.